Patent Publication Number: US-2023156544-A1

Title: Managing measurement gap configurations

Description:
This disclosure relates generally to wireless communications and, more particularly, to managing measurement gap information in certain scenarios involving handover and dual connectivity and certain base station architectures. 
     BACKGROUND 
     This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is 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. 
     A user device (or user equipment, commonly denoted by acronym “UE”) in some cases can concurrently utilize resources of multiple network nodes, e.g., base stations, interconnected by a backhaul. When these network nodes support the same radio access technology (RAT) or different RATs, this type of connectivity is referred to as Dual Connectivity (DC) or Multi-Radio DC (MR-DC), respectively. When a UE operates in DC or MR-DC, one base station operates as a master node (MN), and the other base station operates as a secondary node (SN). The backhaul can support an Xn interface, for example. 
     The MN can provide a control-plane connection and a user-plane connection to a core network (CN), whereas the SN generally provides a user-plane connection. The cells associated with the MN define a master cell group (MCG), and the cells associated with the SN define a secondary cell group (SCG). The UE and the base stations MN and SN can use signaling radio bearers (SRBs) to exchange radio resource control (RRC) messages, as well as non-access stratum (NAS) messages. 
     There are several types of SRBs that a UE can use when operating in DC. SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and to embed RRC messages related to the SN, and can be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN, and can be referred to as an SCG SRB. Split SRBs allow the UE to exchange RRC messages directly with the MN using radio resources of the MN, the SN, or both of the MN and SN. Further, the UE and the base stations (e.g., MN and SN) use data radio bearers (DRBs) to transport data on a user plane. DRBs terminated at the MN and using the lower-layer resources of only the MN can be referred as MCG DRBs, DRBs terminated at the SN and using the lower-layer resources of only the SN can be referred as SCG DRBs, and DRBs terminated at the MCG but using the lower-layer resources of both the MN and the SN can be referred to as split DRBs. 
     A base station (e.g., MN, SN) and/or the CN in some cases causes the UE to transition from one state of the Radio Resource Control (RRC) protocol to another state. More particularly, the UE can operate in an idle state (e.g., EUTRA-RRC_IDLE, NR-RRC IDLE), in which the UE does not have a radio connection with a base station; a connected state (e.g., EUTRA-RRC_CONNECTED, NR-RRC CONNECTED), in which the UE has a radio connection with the base station; or an inactive state (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE), in which the UE has a suspended radio connection with the base station. 
     In some scenarios, a UE can operate in the connected state and subsequently transition to the inactive state. Generally speaking, in the inactive state, the radio connection between the UE and the radio access network (RAN) is suspended. In response to a network-triggering event, such as when a base station pages the UE (e.g., for an incoming phone call), or when the UE is otherwise triggered to send data (e.g., outgoing phone call, browser launch), the UE can then transition back to the connected state. To carry out the transition, the UE can request that the base station resumes the suspended radio connection (e.g., by sending an RRC Resume Request message), so that the base station can configure the UE to again operate in the connected state. 
     Recently, 3GPP introduced the changes described in documents R2-2004807 and R2-2004811, according to which a UE can transmit a measurement gap capability (i.e., NeedForGapsInfoNR information element (IE)). Meanwhile, 3GPP introduced the changes described in documents in a folder in https://www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_110-e/Inbox/Drafts/%5BOffline-028%5D%5BOther%5D%20Inter-Freq%20measurements%20without%20Gaps%20(Huawei)/CR, according to which a UE can transmit a measurement gap capability (i.e., interFrequencyMeas-Nogap-r16 field). The NeedForGapsInfoNR IE indicates whether a UE requires measurement gaps (simplified as gaps in some instances hereinafter) to perform measurements on a target frequency band. This may occur when a UE cannot measure a target band that is a carrier frequency of a target cell at the same time as transmitting and/or receiving on the serving cell(s). In some scenarios, the UE can transmit the NeedForGapsInfoNR IE to a gNB in an RRC response message (i.e., RRCReconfiguration or RRCResumeComplete message) during an RRC procedure (i.e., RRC reconfiguration procedure or RRC resume procedure). In other scenarios, the UE can transmit the NeedForGapsInfoNR IE to an eNB or ng-eNB in an UECapabilityInformation message during a UE Capability Enquiry procedure. The UE can provide the NeedForGapsInfo)NR IE for NR intra-frequency measurements and/or NR inter-frequency measurement. 
     The interFrequencyMeas-NoGap-R16 field indicates that the UE can perform inter-frequency synchronization signal block (SSB) based measurements without measurement gaps if the SSB is completely contained in the active bandwidth part (BWP) of the UE as specified in 3GPP Technical Specification 38.133. In some scenarios, the UE can transmit the interFrequencyMeas-NoGap-r16 field to a gNB in an UECapabilityInformation message during a UE Capability Enquiry procedure. 
     However, it is unclear how distributed network devices are to manage the measurement gap capability information and which devices are responsible for determining whether to generate measurement gap configurations. 
     For example, in cases involving a disaggregated gNB architecture, a central unit (CU) of the gNB receives the RRC response message including the NeedForGapsInfoNR IE, while a distributed unit (DU) of the gNB is not aware of the NeedForGapsInfoNR IE. As a result, the DU always configures measurement gaps for the UE for NR intra-frequency measurement and/or NR inter-frequency measurement, even if the NeedForGapsInfoNR IE indicates that the UE is capable of gapless measurement on a particular frequency or band. Consequently, the DU does not schedule transmissions to the UE in the measurement gaps because, according to the DU logic, the UE is not capable of receiving transmissions from the DU while performing measurements in the measurement gaps. This results in inefficient scheduling of transmissions to the UE, and, in turn, sub-optimal UE performance 
     As another example, a UE may transmit the NeedForGapsInfoNR IE to a source gNB but, after a handover of the UE from the source gNB to a target gNB, the target gNB does is not aware of the NeedForGapsInfoNR IE. Therefore, the target gNB conservatively configures measurement gaps for the UE for NR intra-frequency measurements and/or NR inter-frequency measurements even though the UE previously indicated to the source gNB that it is capable of gapless measurement. This results in similar inefficiencies to those discussed above. 
     As yet another example, in dual connectivity scenarios, a UE can provide the NeedForGapsInfoNR IE only to an MN and not to an SN. Further, the NeedForGapsInfoNR IE only indicates measurement gap capability for NR intra-frequency measurements and/or NR inter-frequency measurements configured by the MN. The UE that is in dual connectivity with the MN and the SN thus cannot indicate a NeedForGapsInfoNR IE for NR intra-frequency measurements and/or NR inter-frequency measurements configured by the SN. Therefore, the SN has to conservatively configure measurement gaps for the UE for NR intra-frequency measurements and/or NR inter-frequency measurements even though the UE is capable of gapless measurement. As a result, the MN may unnecessarily omit scheduling transmissions during measurement gaps, resulting in similar inefficiencies to those discussed above. 
     SUMMARY 
     A RAN of this disclosure communicates with a UE and includes at least two network nodes. A first network node can receive a measurement gap capability of the UE and transmit an indication of the measurement gap capability to a second network node. In dual connectivity scenarios, a network node operating as an SN can receive the measurement gap capability directly from the UE. In some scenarios, these two network nodes are a CU and a DU operating as part of a distributed base station. In other scenarios, these two network nodes are different base stations, such as a source base station (S-BS) and a target base station (T-BS) of a handover procedure, or an MN and an SN. 
     In some scenarios, the indication of the measurement gap capability may be an information element (IE), a field, a flag, etc. that specifies the measurement gap capability of the UE (e.g., a NeedForGapsInfoNR IE). In other scenarios, the first network node may determine, based on the measurement gap capability, whether the UE requires measurement gaps for a particular frequency and, if so, transmit measurement timing information (e.g., SMTC timing information) to the second network node. 
     Based on the received indication of the measurement gap capability, the second network node can determine whether to generate a measurement gap configuration for the UE. For example, if the second network node receives the measurement gap capability, the second network node can determine whether the UE requires measurement gaps for a target band and, if so, generate a measurement gap configuration when needed. If the second network node receives measurement timing information, the second network node generates a measurement gap configuration in accordance with the timing information. The second network node provides an indication of whether the second network node generated the measurement gap configuration by, for example, including or excluding the measurement gap configuration in a message to the first network node. In dual connectivity scenarios, the second network node operating as an SN can provide the indication directly to the UE via a radio interface. As used in this disclosure, providing an indication can correspond to providing an explicit indication (e.g., by explicitly providing an IE), or to providing an implicit indication (e.g., by not including an IE in a message responding to a request for the IE). 
     An example embodiment of the techniques of this disclosure is a method in a first network node of a RAN for managing measurement gap information. The method can be implemented by processing hardware and includes receiving, at the first network node from a second network node of the RAN, an indication of a measurement gap capability of the UE in communication with the RAN. The method also includes determining, by processing hardware and based on the indication of the measurement gap capability, whether to generate a measurement gap configuration for the UE. Further, the method includes providing, to the second network node, an indication of whether the first network node generated the measurement gap configuration for the UE. 
     Another example embodiment of these techniques is a method in a first network node of a RAN for managing measurement gap information. The method includes receiving an information element specifying a measurement gap capability of a user equipment (UE) in communication with the RAN. The method also includes transmitting, to a second network node, an indication of the measurement gap capability. Further, the method includes receiving, from the second network node, an indication of whether the second network node generated a measurement gap configuration for the UE. 
     Yet another example embodiment of these techniques is a network node including processing hardware and configured to execute the methods above. 
     Another example embodiment of these techniques is a method in a UE for managing gap measurement. The method can be implemented by processing hardware and includes receiving, from a RAN, a configuration the UE is to use to report a measurement gap capability. The method also includes determining that the configuration specifies at least one frequency band unsupported at the UE. The method further includes generating an indication of a measurement gap capability based on the received configuration and transmitting the indication of the measurement gap capability to the RAN. 
     A further example embodiment of these techniques is a UE including processing hardware and configured to execute the method above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing measurement gap configurations; 
         FIG.  1 B  is another block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing measurement gap configurations; 
         FIG.  1 C  is a block diagram of an example base station in which a central unit (CU) and a distributed unit (DU) that can operate in the system of  FIG.  1 A  or  FIG.  1 B ; 
         FIG.  2    is a block diagram of an example protocol stack according to which the UE of  FIG.  1 A  communicates with base stations; 
         FIG.  3 A  is a messaging diagram of an example scenario in which a CU provides a measurement gap capability of a UE to a DU, and the DU generates a measurement gap configuration in response to the measurement gap capability, in accordance with the techniques of this disclosure; 
         FIG.  3 B  is a messaging diagram of an example scenario similar to the scenario of  FIG.  3 A , but with the DU determining not to generate a measurement gap configuration in response to the measurement gap capability; 
         FIG.  3 C  is a messaging diagram of an example scenario similar to the scenario of  FIG.  3 A , but in which the CU, based on the measurement gap capability of the UE, provides information to the DU, and the DU generates a measurement gap configuration in response to receiving the information; 
         FIG.  3 D  is a messaging diagram of an example scenario similar to the scenario of  FIG.  3 C , but with the CU determining not to request the DU to configure gaps for the UE or determining to request the DU to release gaps previously configured for the UE, based on the measurement gap capability of the UE; 
         FIG.  3 E  is a messaging diagram of an example scenario similar to the scenario of  FIG.  3 A , with the DU determining whether the UE requires gaps based on a UE capability; 
         FIG.  3 F  is a messaging diagram of an example scenario similar to the scenario of  FIG.  3 E , with the CU determining whether the UE requires gaps based on a UE capability; 
         FIG.  4 A  is a messaging diagram of an example handover scenario in which a source base station (S-BS) provides a measurement gap capability of a UE to a target base station (T-BS), and the T-BS determines whether to generate a measurement gap configuration based on the measurement gap capability, in accordance with the techniques of this disclosure; 
         FIG.  4 B  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 A , in which a CU of the T-BS provides the measurement gap capability to a DU of the T-BS, and the DU generates a measurement gap configuration in response to the measurement gap capability; 
         FIG.  4 C  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 B , but with the DU determining not to generate a measurement gap configuration in response to the measurement gap capability; 
         FIG.  4 D  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 B , but in which the CU of the T-BS, based on the measurement gap capability of the UE, provides information to the DU of the T-BS, and the DU generates a measurement gap configuration in response to receiving the information; 
         FIG.  4 E  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 D , but with the CU of the T-BS determining not to request the DU to configure gaps for the UE or determining to request the DU to release gaps previously configured for the UE, based on the measurement gap capability of the UE; 
         FIG.  4 F  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 B , but with the handover being from a source DU (S-DU) of a base station to a target DU (T-DU) of the base station; 
         FIG.  4 G  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 C , but with the handover being from an S-DU of a base station to a T-DU of the base station; 
         FIG.  4 H  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 D , but with the handover being from an S-DU of a base station to a T-DU of the base station; 
         FIG.  4 I  is a messaging diagram of an example handover scenario similar to the scenario of  FIG.  4 E , but with the handover being from an S-DU of a base station to a T-DU of the base station; 
         FIG.  5 A  is a messaging diagram of an example scenario in which an SN receives the measurement gap capability of a UE operating in MR-DC from an MN, and the SN determines whether to generate a measurement gap configuration based on the measurement gap capability, in accordance with the techniques of this disclosure; 
         FIG.  5 B  is a messaging diagram of an example scenario similar to the scenario of  FIG.  5 A , but in which the SN receives the measurement gap capability directly from the UE; 
         FIG.  5 C  is a messaging diagram of an example scenario similar to the scenario of  FIG.  5 A , in which a CU of the SN provides a measurement gap capability or information to a DU of the SN, in accordance with which the DU determines whether to generate a measurement gap configuration; 
         FIG.  5 D  is a messaging diagram of an example scenario similar to the scenario of  FIG.  5 C , but with the CU providing the measurement gap capability or information to the DU during the SN addition procedure; 
         FIG.  6 A  is a messaging diagram of an example scenario in which a source base station (S-BS) suspends an RRC connection with a UE, and the UE resumes an RRC connection with a target base station (T-BS), with the UE providing a measurement gap capability of the UE to the T-BS, in accordance with the techniques of this disclosure; 
         FIG.  6 B  is a messaging diagram of an example scenario similar to the scenario of  FIG.  6 A , but with the S-BS providing a measurement gap capability of the UE to the T-BS; 
         FIG.  7    is a messaging diagram of an example scenario in which a source MN (S-MN) and source SN (S-SN) suspend an RRC connection with a UE, and the UE resumes an RRC connection with a target MN (T-MN) and target SN (T-SN), with the S-MN providing a measurement gap capability of the UE to the T-MN, in accordance with the techniques of this disclosure; 
         FIG.  8    is a flow diagram of an example method for managing measurement gap capability information, which can be implemented in a CU of this disclosure; 
         FIG.  9 A  is a flow diagram of an example method for determining whether to generate a measurement gap configuration, which can be implemented in a DU of this disclosure; 
         FIG.  9 B  is a flow diagram of another example method for determining whether to generate a measurement gap configuration, which can be implemented in a DU of this disclosure; 
         FIG.  10    is a flow diagram of an example method for determining whether to include SMTC information indicating a measurement gap capability of a UE in a message to a DU, which can be implemented in a CU of this disclosure; 
         FIG.  11    is a flow diagram of an example method for managing measurement gap capability information during handover scenarios, which can be implemented in an S-BS of this disclosure; 
         FIG.  12    is a flow diagram of an example method for managing measurement gap capability information following suspending an RRC connection, which can be implemented in an S-BS of this disclosure; 
         FIG.  13    is a flow diagram of an example method for generating measurement gap capability information, which can be implemented in a UE of this disclosure; 
         FIG.  14    is a flow diagram of an example method for requesting measurement gap capability information from a UE, which can be implemented in a base station of this disclosure; 
         FIG.  15    is a flow diagram of an example method for managing measurement gap information, which can be implemented in a network node of this disclosure; and 
         FIG.  16    is a flow diagram of another example method for managing measurement gap information, which can be implemented in a network node of this disclosure. 
         FIG.  17    is a flow diagram of an example method for managing gap measurement, which can be implemented in a UE of this disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     As discussed in detail below, network nodes of a radio access network (RAN) in communication with a UE can implement the techniques disclosed herein to manage measurement gap configurations in scenarios involving distributed base station architectures and scenarios involving handover and dual connectivity for example. Prior to discussing these techniques, example communication systems which can implement these techniques are considered with reference to  FIGS.  1 A- 1 C . 
     Referring first to  FIG.  1 A , an example wireless communication system  100  includes a UE  102 , a base station (BS)  104 A, a base station  106 A, and a core network (CN)  110 . The base stations  104 A and  106 A can operate in a RAN  105  connected to the same core network (CN)  110 . The CN  110  can be implemented as an evolved packet core (EPC)  111  or a fifth generation (5G) core (5GC)  160 , for example. 
     Among other components, the EPC  111  can include a Serving Gateway (S-GW)  112  and a Mobility Management Entity (MME)  114 . The S-GW  112  in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME  114  is configured to manage authentication, registration, paging, and other related functions. The 5GC  160  includes a User Plane Function (UPF)  162  and an Access and Mobility Management (AMF)  164 , and/or Session Management Function (SMF)  166 . Generally speaking, the UPF  162  is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF  164  is configured to manage authentication, registration, paging, and other related functions, and the SMF  166  is configured to manage PDU sessions. 
     As illustrated in  FIG.  1 A , the base station  104 A supports a cell  124 A, and the base station  106 A supports a cell  126 A. The cells  124 A and  126 A can partially overlap, so that the UE  102  can communicate in DC with the base station  104 A and the base station  106 A operating as a master node (MN) and a secondary node (SN), respectively. To directly exchange messages during DC scenarios and other scenarios discussed below, the MN  104 A and the SN  106 A can support an X2 or Xn interface. In general, the CN  110  can connect to any suitable number of base stations supporting NR cells and/or EUTRA cells. An example configuration in which the EPC  110  is connected to additional base stations is discussed below with reference to  FIG.  1 B . 
     The base station  104 A is equipped with processing hardware  130  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  130  in an example implementation includes an RRC controller  132  configured to manage RRC configurations specified in one or more particular RRC release and/or versions, when the base station  104 A operates as an MN. The processing hardware  130  further can implement a Gap configuration controller  134  configured to implement some or all of the techniques for managing gap measurements at a UE discussed in this disclosure. Depending on the implementation, the Gap configuration controller  134  can operate as a component of the RRC controller  132 , as a component separate from the RRC controller  132 , or as a component only partially implemented in the RRC controller  132 . 
     The base station  106 A is equipped with processing hardware  140  that can also 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  140  in an example implementation includes an RRC controller  142  configured to manage RRC configurations specified in one or more particular RRC release and/or versions, when the base station  106 A operates as an SN, and a Gap configuration controller  144  similar to the Gap configuration controller  134 . In some implementations, the Gap configuration controllers  134  and  144  each implement functionality of an MN and an SN because each of the base stations  104 A and  106 A can operate as an MN or an SN in different scenarios. 
     Still referring to  FIG.  1 A , the UE  102  is equipped with processing hardware  150  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  150  in an example implementation includes a UE RRC controller  152  configured to manage RRC configurations. 
     More particularly, the RRC controllers  132 ,  142 , and  152  can implement at least some of the techniques discussed with reference to the messaging and flow diagrams below to manage RRC configurations. Although  FIG.  1 A  illustrates the RRC controllers  132  and  142  as separate components, in at least some of the scenarios the base stations  104 A and  106 A can have similar implementations and in different scenarios operate as MN or SN nodes. In these implementations, each of the base stations  104 A and  106 A can implement both the RRC controller  132  and the RRC controller  142  to support MN and SN functionality, respectively. 
     In operation, the UE  102  can use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the MN  104 A or the SN  106 A. The UE  102  can receive a radio bearer configuration configuring the radio bearer from the MN  104 A or the SN  106 A. The UE  102  can apply one or more security keys when communicating on the radio bearer, in the uplink (from the UE  102  to a base station) and/or downlink (from a base station to the UE  102 ) direction. The UE in some cases can use different RATs to communicate with the base stations  104 A and  106 A. Although the examples below may refer specifically to specific RAT types, 5G NR or EUTRA, in general the techniques of this disclosure also can apply to other suitable radio access and/or core network technologies. 
       FIG.  1 B  depicts an example wireless communication system  100  in which communication devices can implement these techniques. The wireless communication system  100  includes a UE  102 , a base station  104 A, a base station  104 B, a base station  106 A, a base station  106 B and a core network (CN)  110 . The UE  102  initially connects to the base station  104 A. The BSs  104 B and  106 B may have similar processing hardware as the base station  106 A. The UE  102  initially connects to the base station  104 A. 
     In some scenarios, the base station  104 A can perform immediate SN addition to configure the UE  102  to operate in dual connectivity (DC) with the base station  104 A (via a PCell) and the base station  106 A (via a PSCell other than cell  126 A). The base stations  104 A and  106 A operate as an MN and an SN for the UE  102 , respectively. The UE  102  in some cases can operate using the MR-DC connectivity mode, e.g., communicate with the base station  104 A using 5G NR and communicate with the base station  106 A using EUTRA, or communicate with the base station  104 A using EUTRA and communicate with the base station  106 A using 5G NR. 
     At some point, the MN  104 A can perform an immediate SN change to change the SN of the UE  102  from the base station  106 A (source SN, or “S-SN”) to the base station  104 B (target SN, or “T-SN”) while the UE  102  is communicating in DC with the MN  104 A and the S-SN  106 A. In another scenario, the SN  106 A can perform an immediate PSCell change to change the PSCell of the UE  102  to the cell  126 A. In one implementation, the SN  106 A can transmit a configuration changing the PSCell to cell  126 A to the UE  102  via a signaling radio bearer (SRB) (e.g., SRB3) for the immediate PSCell change. In another implementation, the SN  106 A can transmit a configuration changing the PSCell to the cell  126 A to the UE  102  via the MN  104 A for the immediate PSCell change. The MN  104 A may transmit the configuration immediately changing the PSCell to the cell  126 A to the UE  102  via SRB1. 
     In other scenarios, the base station  104 A can perform a conditional SN Addition procedure to first configure the base station  106 B as a C-SN for the UE  102 , i.e. conditional SN addition or change (CSAC). At this time, the UE  102  can be in single connectivity (SC) with the base station  104 A or in DC with the base station  104 A and the base station  106 A. If the UE  102  is in DC with the base station  104 A and the base station  106 A, the MN  104 A may determine to perform the conditional SN Addition procedure in response to a request received from the base station  106 A or in response to one or more measurement results received from the UE  102  or obtained by the MN  104 A from measurements on signals received from the UE  102 . In contrast to the immediate SN Addition case discussed above, the UE  102  does not immediately attempt to connect to the C-SN  106 B. In this scenario, the base station  104 A again operates as an MN, but the base station  106 B initially operates as a C-SN rather than an SN. 
     More particularly, when the UE  102  receives a configuration for the C-SN  106 B, the UE  102  does not connect to the C-SN  106 B until the UE  102  has determined that a certain condition is satisfied (the UE  102  in some cases can consider multiple conditions, but for convenience only the discussion below refers to a single condition). When the UE  102  determines that the condition has been satisfied, the UE  102  connects to the C-SN  106 B, so that the C-SN  106 B begins to operate as the SN  106 B for the UE  102 . Thus, while the base station  106 B operates as a C-SN rather than an SN, the base station  106 B is not yet connected to the UE  102 , and accordingly is not yet servicing the UE  102 . In some implementations, the UE  102  may disconnect from the SN  106 A to connect to the C-SN  106 B. 
     In yet other scenarios, the UE  102  is in DC with the MN  104 A (via a PCell) and SN  106 A (via a PSCell other than cell  126 A and not shown in  FIG.  1 A ). The SN  106 A can perform conditional PSCell addition or change (CPAC) to configure a candidate PSCell (C-PSCell)  126 A for the UE  102 . If the UE  102  is configured a signaling radio bearer (SRB) (e.g., SRB3) to exchange RRC messages with the SN  106 A, the SN  106 A may transmit a configuration for the C-PSCell  126 A to the UE  102  via the SRB, e.g., in response to one or more measurement results which may be received from the UE  102  via the SRB or via the MN  104 A or may be obtained by the SN  106 A from measurements on signals received from the UE  102 . In case of via the MN  104 A, the MN  104 A receives the configuration for the C-PSCell  126 A. In contrast to the immediate PSCell change case discussed above, the UE  102  does not immediately disconnect from the PSCell and attempt to connect to the C-PSCell  126 A. 
     More particularly, when the UE  102  receives a configuration for the C-PSCell  126 A, the UE  102  does not connect to the C-PSCell  126 A until the UE  102  has determined that a certain condition is satisfied (the UE  102  in some cases can consider multiple conditions, but for convenience only the discussion below refers to a single condition). When the UE  102  determines that the condition has been satisfied, the UE  102  connects to the C-PSCell  126 A, so that the C-PSCell  126 A begins to operate as the PSCell  126 A for the UE  102 . Thus, while the cell  126 A operates as a C-PSCell rather than a PSCell, the SN  106 A may not yet connect to the UE  102  via the cell  126 A. In some implementations, the UE  102  may disconnect from the PSCell to connect to the C-PSCell  126 A. 
     In some scenarios, the condition associated with CSAC or CPAC can be signal strength/quality, which the UE  102  detects on the C-PSCell  126 A of the SN  106 A or on a C-PSCell  126 B of C-SN  106 B, exceeding a certain threshold or otherwise corresponding to an acceptable measurement. For example, when the one or more measurement results the UE  102  obtains on the C-PSCell  126 A are above a threshold configured by the MN  104 A or the SN  106 A or above a pre-determined or pre-configured threshold, the UE  102  determines that the condition is satisfied. When the UE  102  determines that the signal strength/quality on the C-PSCell  126 A of the SN  106 A is sufficiently good (again, measured relative to one or more quantitative thresholds or other quantitative metrics), the UE  102  can perform a random access procedure on the C-PSCell  126 A with the SN  106 A to connect to the SN  106 A. After the UE  102  successfully completes the random access procedure on the C-PSCell  126 A, the C-PSCell  126 A becomes a PSCell  126 A for the UE  102 . The SN  106 A then can start communicating data (user-plane data or control-plane data) with the UE  102  through the PSCell  126 A. In another example, when the one or more measurement results the UE  102  obtains on the C-PSCell  126 B are above a threshold configured by the MN  104 A or the C-SN  106 B or above a pre-determined or pre-configured threshold, the UE  102  determines that the condition is satisfied. When the UE  102  determines that the signal strength/quality on the C-PSCell  126 B of the C-SN  106 B is sufficiently good (again, measured relative to one or more quantitative thresholds or other quantitative metrics), the UE  102  can perform a random access procedure on the C-PSCell  126 B with the C-SN  106 B to connect to the C-SN  106 B. After the UE  102  successfully completes the random access procedure on the C-PSCell  126 B, the C-PSCell  126 B becomes a PSCell  126 B for the UE  102  and the C-SN  106 B becomes an SN  106 B. The SN  106 B then can start communicating data (user-plane data or control-plane data) with the UE  102  through the PSCell  126 B. 
     In various configurations of the wireless communication system  100 , the base station  104 A can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station  106 A or  106 B can be implemented as a secondary gNB (SgNB) or a candidate SgNB (C-SgNB). The UE  102  can communicate with the base station  104 A and the base station  106 A or  106 B ( 106 A/B) via the same RAT such as EUTRA or NR, or different RATs. When the base station  104 A is an MeNB and the base station  106 A is an SgNB, the UE  102  can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB. In this scenario, the MeNB  104 A may or may not configure the base station  106 B as a C-SgNB to the UE  102 . In this scenario, the SgNB  106 A may configure cell  126 A as a C-PSCell to the UE  102 . When the base station  104 A is an MeNB and the base station  106 A is a C-SgNB for the UE  102 , the UE  102  can be in SC with the MeNB. In this scenario, the MeNB  104 A may or may not configure the base station  106 B as another C-SgNB to the UE  102 . 
     In some cases, an MeNB, an SeNB or a C-SgNB is implemented as an ng-eNB rather than an eNB. When the base station  104 A is a Master ng-eNB (Mng-eNB) and the base station  106 A is a SgNB, the UE  102  can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. In this scenario, the MeNB  104 A may or may not configure the base station  106 B as a C-SgNB to the UE  102 . In this scenario, the SgNB  106 A may configure cell  126 A as a C-PSCell to the UE  102 . When the base station  104 A is an Mng-NB and the base station  106 A is a C-SgNB for the UE  102 , the UE  102  can be in SC with the Mng-NB. In this scenario, the Mng-eNB  104 A may or may not configure the base station  106 B as another C-SgNB to the UE  102 . 
     When the base station  104 A is an MgNB and the base station  106 A/B is an SgNB, the UE  102  may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. In this scenario, the MeNB  104 A may or may not configure the base station  106 B as a C-SgNB to the UE  102 . In this scenario, the SgNB  106 A may configure cell  126 A as a C-PSCell to the UE  102 . When the base station  104 A is an MgNB and the base station  106 A is a C-SgNB for the UE  102 , the UE  102  may be in SC with the MgNB. In this scenario, the MgNB  104 A may or may not configure the base station  106 B as another C-SgNB to the UE  102 . 
     When the base station  104 A is an MgNB and the base station  106 A/B is a Secondary ng-eNB (Sng-eNB), the UE  102  may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB. In this scenario, the MgNB  104 A may or may not configure the base station  106 B as a C-Sng-eNB to the UE  102 . In this scenario, the Sng-eNB  106 A may configure cell  126 A as a C-PSCell to the UE  102 . When the base station  104 A is an MgNB and the base station  106 A is a candidate Sng-eNB (C-Sng-eNB) for the UE  102 , the UE  102  may be in SC with the MgNB. In this scenario, the MgNB  104 A may or may not configure the base station  106 B as another C-Sng-eNB to the UE  102 . 
     The base stations  104 A,  104 B,  106 A, and  106 B can connect to the same core network (CN)  110  which can be an evolved packet core (EPC)  111  or a fifth-generation core (5GC)  160 . The base station  104 A can be implemented as an eNB supporting an S1 interface for communicating with the EPC  111 , an ng-eNB supporting an NG interface for communicating with the 5GC  160 , or as a base station that supports the NR radio interface as well as an NG interface for communicating with the 5GC  160 . The base station  106 A can be implemented as an EN-DC gNB (en-gNB) with an S1 interface to the EPC  111 , an en-gNB that does not connect to the EPC  111 , a gNB that supports the NR radio interface as well as an NG interface to the 5GC  160 , or a ng-eNB that supports an EUTRA radio interface as well as an NG interface to the 5GC  160 . To directly exchange messages during the scenarios discussed below, the base stations  104 A,  104 B,  106 A, and  106 B can support an X2 or Xn interface. 
     As illustrated in  FIG.  1 B , the base station  104 A supports a cell  124 A, the base station  104 B supports a cell  124 B, the base station  106 A supports a cell  126 A, and the base station  106 B supports a cell  126 B. The cells  124 A and  126 A can partially overlap, as can the cells  124 A and  124 B, so that the UE  102  can communicate in DC with the base station  104 A (operating as an MN) and the base station  106 A (operating as an SN) and, upon completing an SN change, with the base station  104 A (operating as MN) and the SN  104 B. More particularly, when the UE  102  operates in DC with the base station  104 A and the base station  106 A, the base station  104 A operates as an MeNB, an Mng-eNB, or an MgNB, and the base station  106 A operates as an SgNB, or an Sng-eNB. The cells  124 A and  126 B can partially overlap. When the UE  102  is in SC with the base station  104 A, the base station  104 A operates as an MeNB, an Mng-eNB, or an MgNB, and the base station  106 B operates as a C-SgNB, or a C-Sng-eNB. When the UE  102  operates in DC with the base station  104 A and the base station  106 A, the base station  104 A operates as an MeNB, an Mng-eNB, or an MgNB, the base station  106 A operates as an SgNB or an Sng-eNB, and the base station  106 B operates as a C-SgNB or a C-Sng-eNB. 
     In general, the wireless communication network  100  can include any suitable number of base stations supporting NR cells and/or EUTRA cells. More particularly, the EPC  111  or the 5GC  160  can be connected to any suitable number of base stations supporting NR cells and/or EUTRA cells. Although the examples below refer specifically to specific CN types (EPC, 5GC) and RAT types (5G NR and EUTRA), in general the techniques of this disclosure also can apply to other suitable radio access and/or core network technologies such as sixth generation (6G) radio access and/or 6G core network or 5G NR-6G DC. 
     As indicated above, the wireless communication system  100  can support various procedures (e.g., DAPS handover, DAPS PSCell change, etc.) and modes of operation (e.g., SC or DC). Example operation of various procedures that can be implemented in the wireless communication system  100  will now be described. 
     In some implementations, the wireless communication system  100  supports a legacy handover preparation procedure (i.e., a non-DAPS handover preparation procedure). In one scenario, for example, the base station  104 A can perform a non-DAPS handover preparation procedure to configure the UE  102  to handover from a cell  124 A of the base station  104 A to a cell  124 B of the base station  104 B. In this scenario, the base station  104 A and the base station  104 B operate as a source base station (S-BS) or a source MN (S-MN), and a target base station (T-BS) or a target MN (T-MN), respectively. In the non-DAPS handover preparation procedure, the base station  104 A sends a Handover Request message to the base station  104 B. In response to the Handover Request message, the base station  104 B includes configuration parameters configuring radio resources for the UE  102  in a handover command message, includes the handover command message in a Handover Request Acknowledge message, and sends the Handover Request Acknowledge message to the base station  104 . In turn, the base station  104 A transmits the handover command message to the UE  102  and subsequently discontinues (or stops) transmitting data to or receiving data from the UE  102 . 
     Upon receiving the handover command message, the UE  102  hands over to the base station  104 B via cell  124 B and communicates with the base station  104 B using the configuration parameters in the handover command message. Particularly, in response to the handover command message, the UE  102  disconnects from the cell  124 A (or the base station  104 A), performs a random access procedure with the base station  104 B via the cell  124 B, and transmits a handover complete message to the base station  104 B via the cell  124 B. 
     In some implementations, the wireless communication system  100  supports a DAPS handover preparation procedure. In one scenario for example, the base station  104 A can perform a DAPS handover preparation procedure to configure the UE  102  to hand over from a cell  124 A of the base station  104 A to a cell  124 B of the base station  104 B. In this scenario, the base station  104 A and the base station  104 B operate as an S-BS or an S-MN, and a T-BS or a T-MN, respectively. In the DAPS handover preparation procedure, the base station  104 A sends a Handover Request message to the base station  104 B. In some implementations, the base station  104 A can explicitly request DAPS handover in the Handover Request message, e.g., by including a DAPS indicator in the Handover Request message. In response to the Handover Request message, and to accept the request for DAPS handover, the base station  104 B includes configuration parameters configuring radio resources for the UE  102  in a handover command, includes the handover command message in a Handover Request Acknowledge message, and sends the Handover Request Acknowledge message to the base station  104 A. In some implementations, the base station  104 B can indicate DAPS handover in the handover command message, e.g., by including a DAPS handover configuration or a DAPS handover indicator in the handover command message, or can include an indicator in the Handover Request Acknowledge message. In turn, the base station  104 A transmits the handover command message to the UE  102 . 
     Upon receiving the handover command message, the UE  102  hands over to the base station  104 B via cell  124 B and communicates with the base station  104 B using the configuration parameters in the handover command message. Particularly, in response to the handover command message, whereas in the non-DAPS handover preparation procedure the UE  102  disconnects from the cell  124 A (or the base station  104 ), the UE  102  in the DAPS handover preparation procedure maintains the connection to the base station  104  via cell  124 , performs a random access procedure with the base station  104 B via cell  124 B, and transmits a handover complete message to the base station  104 B via cell  124 B. 
     In maintaining the connection to the base station  104 A via cell  124 A in the DAPS handover preparation procedure, the UE  102  effectively has two links, i.e., a source MCG link with the base station  104 A and a target MCG link with the base station  104 B. The UE  102  can continue receiving data (i.e., downlink data) from the base station  104 A until the UE  102  receives an indication from the base station  104 B to release the source MCG link with the base station  104 A. The UE  102  can continue transmitting data (e.g., new uplink data transmission or retransmission of PDCP SDUs) to the base station  104 A until the UE  102  either successfully completes the random access procedure with the base station  104 B or receives the indication from the base station  106 B to release the MCG link with the base station  104 A. 
     In some implementations, in the handover preparation procedure scenarios above, the wireless communication system  100  supports DC operation. In one scenario, for example, after the UE  102  connects to the base station  104 A, the base station  104 A can perform an SN addition procedure to add the base station  106 A as an SN, thereby configuring the UE  102  to operate in DC with the base stations  104 A and  106 A. At this point, the base stations  104  and  106 A operate as an MN and an SN, respectively. Later on, the MN  104 A can initiate the non-DAPS or DAPS handover preparation procedures to handover the UE  102  to the T-MN  104 B. 
     In some implementations, the wireless communication system  100  supports a legacy PSCell change preparation procedure (i.e., a non-DAPS PSCell change preparation procedure). In one scenario, for example, while the UE  102  is in DC with the MN  104 A and the SN  106 A, the MN  104 A determines to change the SN of the UE  102  from the base station  106 A (which may be referred to as the source SN or S-SN) to the base station  106 B (which may be referred to as the target SN or T-SN) as part of the non-DAPS PSCell change procedure. The UE  102  stops communicating with the S-SN  106 A via PSCell  126 A and attempts to connect to the T-SN  106 B via T-PSCell  126 B after receiving the configuration for the T-PSCell  126 B. 
     In some implementations, the wireless communication system  100  supports DAPS PSCell change. In one scenario, for example, while the UE  102  is in DC with the MN  104 A and the SN  106 A, the MN  104 A determines to change the SN of the UE  102  from the base station  106 A (which may be referred to as the source SN or S-SN) to the base station  106 B (which may be referred to as the target SN or T-SN) as part of the DAPS PSCell change procedure. The UE  102  continues communicating with the S-SN  106 A via PSCell  126 A while attempting to connect to the T-SN  106 B via T-PSCell  126 B after receiving the configuration for the T-PSCell  126 B. After the T-PSCell  126 B begins to operate as the PSCell  126 B for the UE  102 , the UE  102  stops communicating with the S-SN  106 A via PSCell  126 A. 
     In different configurations or scenarios of the wireless communication system  100 , the base station  104 A,  104 B can operate as an MeNB, an Mng-eNB, or an MgNB and the base station  106 A,  106 B can operate as an SgNB or an Sng-eNB. The UE  102  can communicate with the base station  104 A or  104 B and the base station  106 A or  106 B via the same radio access technology (RAT), such as EUTRA or NR, or via different RATs. 
     When the base station  104 A is an MeNB and the base station  106 A is an SgNB, the UE  102  can be in EUTRA-NR DC (EN-DC) with the MeNB  104 A and the SgNB  106 A. When the base station  104 A is an Mng-eNB and the base station  106 A is an SgNB, the UE  102  can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB  104 A and the SgNB  106 A. When the base station  104 A is an MgNB and the base station  106 A is an SgNB, the UE  102  can be in NR-NR DC (NR-DC) with the MgNB  104 A and the SgNB  106 A. When the base station  104 A is an MgNB and the base station  106 A is an Sng-eNB, the UE  102  can be in NR-EUTRA DC (NE-DC) with the MgNB  104 A and the Sng-eNB  106 A. 
       FIG.  1 C  depicts an example distributed implementation of a base station such as the base station  104 A,  104 B,  106 A, or  106 B. The base station in this implementation can include a central unit (CU)  172  and one or more distributed units (DUs)  174 . The CU  172  is equipped with processing hardware 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. In one example, the CU  172  is equipped with the processing hardware  130 . In another example, the CU  172  is equipped with the processing hardware  140 . The processing hardware  140  in an example implementation includes an (C-)SN RRC controller  142  configured to manage or control one or more RRC configurations and/or RRC procedures when the base station  106 A operates as an SN or a candidate SN (C-SN). The base station  106 B can have hardware same as or similar to the base station  106 A. The DU  174  is also equipped with processing hardware 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. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the base station  106 A operates as an MN, an SN or a candidate SN (C-SN). The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures. 
     The CU  172  and the DUs  174  in some implementations include separate instances of a Gap configuration controller  134  or  144  to implement CU gap configuration management and DU gap configuration management, respectively. 
       FIG.  2    illustrates, in a simplified manner, an example radio protocol stack  200  according to which the UE  102  may communicate with an eNB/ng-eNB or a gNB (e.g., one or more of the base stations  104 A,  104 B,  106 A,  106 B). In the example stack  200 , a physical layer (PHY)  202 A of EUTRA provides transport channels to the EUTRA MAC sublayer  204 A, which in turn provides logical channels to the EUTRA RLC sublayer  206 A. The EUTRA RLC sublayer  206 A in turn provides RLC channels to the EUTRA PDCP sublayer  208  and, in some cases, to the NR PDCP sublayer  210 . Similarly, the NR PHY  202 B provides transport channels to the NR MAC sublayer  204 B, which in turn provides logical channels to the NR RLC sublayer  206 B. The NR RLC sublayer  206 B in turn provides RLC channels to the NR PDCP sublayer  210 . The UE  102 , in some implementations, supports both the EUTRA and the NR stack as shown in  FIG.  2   , to support handover between EUTRA and NR base stations and/or to support DC over EUTRA and NR interfaces. Further, as illustrated in  FIG.  2   , the UE  102  can support layering of NR PDCP sublayer  210  over the EUTRA RLC sublayer  206 A. 
     The EUTRA PDCP sublayer  208  and the NR PDCP sublayer  210  receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer  208  or  210 ) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer  206 A or  206 B) that can be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.” 
     On a control plane, the EUTRA PDCP sublayer  208  and the NR PDCP sublayer  210  can provide SRBs to exchange RRC messages, for example. On a user plane, the EUTRA PDCP sublayer  208  and the NR PDCP sublayer  210  can provide DRBs to support data exchange. 
     In scenarios where the UE  102  operates in EUTRA/NR DC (EN-DC), with the base station  104 A operating as an MeNB and the base station  106 A operating as an SgNB, the wireless communication system  100  can provide the UE  102  with an MN-terminated bearer that uses the EUTRA PDCP sublayer  208 , or an MN-terminated bearer that uses the NR PDCP sublayer  210 . The wireless communication system  100  in various scenarios can also provide the UE  102  with an SN-terminated bearer, which uses only the NR PDCP sublayer  210 . The MN-terminated bearer can be an MCG bearer, a SCG bearer, or a split bearer. The SN-terminated bearer can be, an MCG bearer, an SCG bearer or a split bearer. The MN-terminated bearer can be an SRB (e.g., SRB1 or SRB2) or a DRB. The SN-terminated bearer can an SRB or a DRB. 
     Next, several example scenarios in which a UE and/or a base station manage measurement gap information are discussed with reference to  FIGS.  3 A- 7   . In particular,  FIG.  3    (i.e.,  3 A through  3 D) corresponds to communication scenarios in which a distributed base station having a CU and a DU communicates with a UE.  FIG.  4    (i.e.,  4 A through  4 I) corresponds to handover scenarios in which a base station initiates a handover procedure for a UE.  FIG.  5    (i.e.,  5 A through  5 D) corresponds to DC scenarios in which a base station initiates an SN addition procedure for a UE.  FIG.  6    (i.e.,  6 A and  6 B) and  FIG.  7    correspond to resume scenarios in which a base station initiates a Retrieve UE Context procedure for a UE during an RRC resume procedure with the UE. 
     Referring first to  FIG.  3 A , the base station  104 A in a scenario  300 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Initially, the UE  102  communicates  302 A data (e.g., uplink (UL) PDUs and/or downlink (DL) PDUs) with the base station  104 A (i.e., the CU  172  and DU  174 ) via the cell  124 A. Later in time, the CU  172  initiates an RRC reconfiguration procedure with the UE  102  by sending  304 A an RRC reconfiguration including a first need for gaps configuration (NeedForGapsConfig) to the DU  174  which in turn transmits  306 A the RRC reconfiguration message to the UE  102 . The NeedForGapsConfig is a configuration the UE  102  can use to report measurement gap requirement information to the RAN  105 . 
     In response to the first NeedForGapsConfig, the UE  102  includes a first need for gaps information element (NeedForGapsInfo) in an RRC reconfiguration complete message. The NeedForGapsInfo IE indicates measurement gap requirement information for the UE  102 . The UE  102  transmits  308 A the RRC reconfiguration message including the first NeedForGapsInfo to the DU  174  which in turn sends  310 A the RRC reconfiguration message to the CU  172 . The events  304 A,  306 A,  308 A and  310 A are collectively referred to in  FIG.  3 A  as a need for gap information procedure  350 A. 
     In some implementations, the CU  172  may indicate one or more frequency bands, for which the UE  102  is to indicate whether gaps are needed to perform measurements, in the first NeedForGapsConfig. In one implementation, the CU  172  generates a requestTargetBandFilterNR field which includes one or more frequency band indicators (e.g., FreqBandIndicatorNR IEs) indicating the one or more frequency bands and includes the requestTargetBandFilterNR field in the first NeedForGapsConfig. In the first NeedForGapsInfo, the UE  102  indicates whether gaps are needed to perform measurements for the one or more frequency bands. In one implementation, in the first NeedForGapsInfo, the UE  102  does not indicate whether gaps are needed to perform measurements for one or more additional frequency bands not indicated by the CU  172  in the first NeedForGapsConfig. With this implementation, the UE  102  saves power due by not using bits to indicate whether gaps are needed to perform measurements for the one or more additional frequency bands. In another implementation, the UE  102  indicates, in the first NeedForGapsInfo, whether gaps are needed to perform measurements for one or more additional frequency bands not indicated by the CU  172  in the first NeedForGapsConfig. With this implementation, the CU  172  does not need to initiate another need for gap information procedure (similar to  350 A) to request that the UE  102  provide another NeedForGapsInfo indicating whether gaps are needed to perform measurements for one or more additional frequency bands. 
     In other implementations, the CU  172  does not indicate a frequency band in the first NeedForGapsConfig. In one such implementation, if the CU  172  does not indicate a frequency band in the first NeedForGapsConfig, the UE  102  can determine frequency band(s) for which the UE  102  will indicate measurement gap requirements in the first NeedForGapsInfo. The UE  102  can determine the frequency band(s) based on a public land mobile network (PLMN) identity of an operator operating the base station  104 A. For example, the UE  102  may store first band information associated with a first PLMN identity, which indicates first frequency band(s) owned by a first operator identified by the first PLMN identity. The UE  102  can generate the first NeedForGapsInfo which indicates whether gaps are needed to perform measurements for the first frequency band(s) in the first band information if the base station  104 A is operated by the first operator. The UE  102  can store second band information associated to the second PLMN identity, which indicates second frequency band(s) owned by a second operator identified by the second PLMN identity. The UE  102  can generate the first NeedForGapsInfo which indicates whether gaps are needed to perform measurements for the second frequency band(s) in the second band information if the base station  104 A is operated by the second operator. The first and second frequency band(s) can be completely or partially the same or different. 
     Alternatively, the UE  102  can directly store a first NeedForGapsInfo indicating whether gaps are needed to perform measurements for frequency band(s) owned by a first operator identified by a first PLMN identity, and transmit  322 A the RRC reconfiguration complete message including the first NeedForGapsInfo if the base station  104 A is operated by the first operator. The UE  102  can directly store a second NeedForGapsInfo indicating whether gaps are needed to perform measurements for frequency band(s) owned by a second operator identified by a second PLMN identity, and transmit  322 A the RRC reconfiguration complete message including the second NeedForGapsInfo instead of the first NeedForGapsInfo if the base station  104 A is operated by the second operator. Note, the stored first/second NeedForGapsInfo may or may not in the same format as the first/second NeedForGapsInfo transmitted in the RRC reconfiguration message. If the formats are different, the UE  102  converts the stored format to the transmitted format. 
     In another implementation, if the CU  172  does not indicate a frequency band in the first NeedForGapsConfig, the UE  102  indicates whether gaps are needed to perform measurements in the first NeedForGapsInfo for all frequency band(s) the UE supports. 
     In some implementations, the CU  172  transmits  304 A the RRC reconfiguration message after the CU  172  activates security for the UE  102 . That is, the CU  172  requests that the UE  102  provide a NeedForGapsInfo only after activating the security. To activate the security, the CU  172  in one implementation can send a SecurityModeCommand message to the DU  174  which in turn transmits the SecurityModeCommand message to the UE  102 . The UE  102  can send a SecurityModeComplete message to the CU  172  via the DU  174 . In other implementations, the CU  172  can transmit  304 A the RRC reconfiguration message before the CU  172  activates the security. 
     After receiving the first NeedForGapsInfo, the CU  172  sends  312 A a UE Context Modification Request message including the first NeedForGapsInfo to the DU  174 . In some implementations, the first NeedForGapsInfo can be a NeedForGapsInfo for NR information element (NeedForGapsInfoNR) defined in R2-2004807 or R2-2004811. The DU  174  generates  314 A a measurement gap configuration (MeasGapConfig) in response to the first NeedForGapsInfo. In some implementations, the DU  174  can configure gaps in a gap configuration (GapConfig) and includes the GapConfig in the MeasGapConfig because the DU  174  determines the UE  102  needs gaps to perform measurements. In other implementations, the DU  174  can release a GapConfig which was previously configured to the UE  102  at event  302 A because the DU  174  determines, based on the NeedForGapsInfo, that the UE  102  does not need the GapConfig to perform measurements. In such implementations, the MeasGapConfig indicates that the UE  102  should release the previously-configured GapConfig. 
     In the UE Context Modification Request message, the CU  172  in some implementations includes frequency information indicating at least one carrier frequency for which the CU  172  requests the DU  174  to configure measurement gaps, and/or includes synchronization signal (SS)/physical broadcast channel (PBCH) Block Measurement Time Configuration (SMTC) information for the at least one carrier frequency, in a UE Context Modification Request message. The DU  174  generates  314 A the GapConfig according to the frequency information and/or SMTC information in addition to the NeedForGapsInfo. The “carrier frequency” can be referred to as a particular carrier frequency or a particular frequency band in the following description. 
     The DU  174  sends  316 A a UE Context Modification Response message including the MeasGapConfig to the CU  172  in response to the UE Context Modification Request message. In some implementations, the DU  174  does not include the MeasGapConfig in the UE Context Modification Response message. Instead, the DU  174  sends a UE Context Modification Required message including the MeasGapConfig to the CU  172  and the CU  172  sends a UE Context Modification Confirm message to the DU  174  in response. The events  312 A,  314 A and  316 A are collectively referred to in  FIG.  3 A  as a UE Context Modification procedure  360 A. 
     After the CU  172  receives  316 A the MeasGapConfig, the CU  172  sends  318 A an RRC reconfiguration message including the MeasGapConfig to the DU  174  which in turn transmits  320 A the RRC reconfiguration message to the UE  102 . In response to the RRC reconfiguration message, the UE  102  transmits  322 A an RRC reconfiguration complete message to the DU  174  which in turn sends  324 A the RRC reconfiguration complete message to the CU  172 . The events  318 A,  320 A,  322 A and  324 A are collectively referred to in  FIG.  3 A  as a measurement configuration procedure  380 A. 
     After the UE  102  receives the MeasGapConfig, the UE  102  can measure one or more carrier frequencies during gaps configured by the MeasGapConfig. The UE  102  may be configured by the CU  172  to measure the one or more carrier frequencies before, during or after receiving the MeasGapConfig. In some implementations, the CU  172  can include the MeasGapConfig in a first measurement configuration (MeasConfig) and include the first MeasConfig in the RRC reconfiguration message  318 A. In the first MeasConfig, the CU  172  may configure the UE  102  to measure a first carrier frequency in a frequency band using gaps configured in the MeasGapConfig. Alternatively, the CU  172  may perform another measurement configuration procedure similar to event  380 A to transmit the UE  102  a second MeasConfig. The second MeasConfig does not include a MeasGapConfig and configures the UE  102  to measure the first carrier frequency in a frequency band using gaps configured in the MeasGapConfig. The CU  172  may perform an additional measurement configuration procedure similar to event  380 A to transmit the UE  102  a third MeasConfig, which does not include a MeasGapConfig and configures the UE  102  to measure a second carrier frequency in a frequency band using gaps configured in the MeasGapConfig. The first and second carrier frequencies can be in the same frequency band or different frequency bands. 
     In implementations in which the UE  102  receives (i) a first MeasConfig including a MeasGapConfig, and (ii) a second MeasConfig not including a MeasGapConfig, the second MeasConfig does not override the previously-received MeasGapConfig. The UE  102  can continue to use the MeasGapConfig received in the first MeasConfig to configure measurement gaps for target frequencies indicated in the second MeasConfig. 
     In some implementations, the CU  172  can include a second NeedForGapsConfig, which indicates one or more additional frequency bands, in the RRC reconfiguration message  318 A. The UE  102  indicates whether gaps are needed to perform measurements for the one or more additional frequency bands in a third NeedForGapsInfo, and includes the third NeedForGapsInfo in the RRC reconfiguration complete message  322 A. The CU  172  may perform a UE Context Modification procedure similar to event  360 A, where the CU  172  provides the third NeedForGapsInfo to the DU  174  and receives a MeasGapConfig (a second MeasGapConfig) from the DU  174 . The CU  172  can transmit the second MeasGapConfig to the UE  102  in a similar way and the UE  102  can use the second MeasGapConfig, as described above. 
     In other implementations, the CU  172  does not include a NeedForGapsConfig in the RRC reconfiguration message  318 A and the UE  102  does not include a NeedForGapsInfo in the RRC reconfiguration complete message  322 A. In such implementations, instead of including a second NeedForGapsConfig in the RRC reconfiguration message  318 A, the CU  172  can include a second NeedForGapsConfig in an additional need for gap information procedure similar to the procedure  350 A. The CU  172  can also repeat procedures similar to  360 A- 380 A after performing the additional need for gap information procedure. 
     The UE  102  applies the MeasGapConfig above to perform measurements on a carrier frequency which can be configured by the CU  172  as described above. If the MeasGapConfig includes a GapConfig, the UE  102  performs measurements during gaps configured by the GapConfig, for example. The gaps are periods that the UE  102  uses to perform measurements. In another example, if the MeasGapConfig indicates that the UE  102  should release a GapConfig, the UE  102  can perform measurements without using gaps. The UE  102  obtains a measurement result from the measurements, includes the measurement result in a measurement report message, and transmits  326 A a measurement report message to the DU  174 . The DU  174  in turn sends  328 A the measurement report message to the CU  172 . For example, the measurement result can indicate a value of a reference signal received power (RSRP), reference signal received quality (RSRQ), Received Signal Strength Indicator (RSSI), or signal to noise and interference ratio (SINR). According to the measurement result, the CU  172  can decide whether to configure or release an SCell for the UE  102  or handover the UE  102  to another cell. For example, if the measurement result associated with a cell is above a predetermined threshold, the CU  172  can configure the cell as an SCell for the UE  102 . In another example, if the measurement result associated with an SCell exceeds a predetermined threshold, the CU  172  can release the SCell for the UE  102 . In yet another example, if the measurement result associated with a cell is above a predetermined threshold, the CU  172  can configure the UE  102  to handover to the cell. The events  326 A and  328 A are collectively referred to in  FIG.  3 A  as a measurement reporting procedure  390 A. 
     After the need for gap information procedure  350 A, the UE  102  may determine to update the NeedForGapsInfo the UE  102  previously transmitted  308 A to the CU  172 . For example, the UE  102  may determine that the UE  102  needs gaps for a particular frequency band when the previous NeedForGapsInfo indicated the UE  102  did not require gaps. In another example, the UE  102  may determine that the UE  102  does not need gaps for a particular frequency band when the previous NeedForGapsInfo indicated the UE  102  required gaps. To update the NeedForGapsInfo provided at event  308 A, the UE  102  can send a second NeedForGapsInfo in a second RRC reconfiguration complete message in response to a second RRC reconfiguration message received from the CU  172  via the DU  174 . In the second RRC reconfiguration message, the CU  172  may include configuration(s), e.g., physical layer configuration, MAC layer configuration, RLC layer configuration, radio bearer configuration and/or measurement configuration. The CU  172  may or may not include the NeedForGapsConfig in the second RRC reconfiguration message. The second RRC reconfiguration message and the second RRC reconfiguration complete message can also referred to as a second need for gap information procedure. 
     After receiving the second NeedForGapsInfo, the CU  72  can perform a second UE Context Modification procedure to provide the second NeedForGapsInfo to the DU  174 , similar to the UE Context Modification procedure  360 A. If the DU  174  determines to update the MeasGapConfig  316 A according to the second NeedForGapsInfo, the DU  174  sends a second MeasGapConfig to the CU  172  in the second UE Context Modification procedure. Then the CU  172  can send the second MeasGapConfig to the UE  102  in a measurement configuration procedure similar to the measurement configuration  380 A. If the second MeasGapConfig configures gaps, the UE  102  may use the gaps to measure a first carrier frequency (i.e., measure the first carrier frequency during the gaps), in some implementations. If the second MeasGapConfig configures gaps and the UE  102  does not need gaps for measuring a second carrier frequency, the UE  102  may not use the gaps to measure the second carrier frequency, in other implementations. The UE  102  measures the second carrier frequency without using gaps. If the second MeasGapConfig releases the GapConfig configured in the MeasGapConfig  318 A, the UE  102  releases the GapConfig and does not consider gaps configured in the GapConfig are available. The UE  102  may measure a particular carrier frequency without using gaps. 
     In some implementations, the CU  172  can receive a UE capability of the UE  102  from the UE  102  during a UE Capability Transfer procedure at event  302 A. In the UE Capability Transfer procedure, the cu  172  sends a UECapabilityEnquiry message to the DU  174  which in turn transmits the UECapabilityEnquiry message to the UE  102 . The UE  102  transmits a UECapabilityInformation message including the UE capability to the DU  174  which in turn transmits the UECapabilityInformation message to the CU  172 . In other implementations, the CU  172  can receive the UE capability in an Initial UE Context Setup message or in a Handover Request message from a core network (CN)  110  (e.g., MME  114  or AMF  164 ) at event  302 A. In these implementations, the CU  172  transmits a NeedForGapsConfig to the UE  102  if the UE capability indicates that the UE  102  supports providing a NeedForGapsInfo. For example, the UE can include an interRAT-NeedForGapsNR or nr-NeedForGap-Reporting field indicating support for providing a NeedForGapsInfo in the UE capability. If the UE capability indicates that the UE  102  does not support providing a NeedForGapsInfo, the CU  172  does not transmit a NeedForGapsConfig to the UE  102 . In some implementations, the UE capability can be a UE-NR-Capability IE or a UE-MRDC-Capability IE. In yet other implementations, the CU  172  can receive the UE capability from another base station (e.g., base station  104 B), e.g., during a handover preparation procedure (e.g., in a Handover Request message) or a Retrieve UE Context procedure (e.g., in a Retrieve UE Context Response message). 
     In some implementations, the UE  102  may indicate, in the UE capability, one or more frequency bands supported by the UE  102  to communicate with a base station in SC. For example, the UE capability can include a supportedBandListNR field which includes one or more BandNR IE indicating one or more frequency bands supported by the UE  102 . In other implementations, the UE  102  may indicate, in the UE capability, one or more frequency bands supported by the UE  102  for communicating with an MN in DC. For example, the UE capability can include a supportedBandCombinationList field (or BandCombinationList IE) which includes one or more FreqBandIndicatorNR IEs indicating one or more frequency bands supported by the UE  102 . In some implementations, the CU  172  can determine (or select) the one or more frequency bands to include in the NeedForGapsConfig from the frequency bands supported by the UE  102 . In other implementations, the CU  172  can include a frequency band in the NeedForGapsConfig that is not supported by the UE  102 . If the UE  102  does not support a frequency band indicated in the NeedForGapsConfig, the UE  102  in some implementations determines the NeedForGapsConfig is valid and ignores the unsupported frequency band. In this case, in one implementation, the UE  102  does not indicate whether gaps are needed for the unsupported frequency band in the NeedForGapsInfo. In another implementation, the UE  102  can indicate whether gaps are needed for the unsupported frequency band in the NeedForGapsInfo even though the indication is meaningless. 
     In other implementations, if the UE  102  does not support a frequency band indicated in the NeedForGapsConfig, the UE  102  determines the NeedForGapsConfig is invalid. In response to the determination, the UE  102  initiates an RRC connection reestablishment procedure. In the RRC connection reestablishment procedure, the UE  102  transmits an RRCReestablishmentRequest message to the base station  104 A or another base station (e.g., base station  104 B). The UE  102  receives a RRCReestablishment message from the base station  104 A or another base station (e.g., the base station  104 B) in response to the RRCReestablishmentRequest message. The UE  102  can transmit a RRCReestablishmentComplete message to the RRCReestablishment message. 
     To transmit a DL RRC message (e.g., the RRC reconfiguration message, the SecurityModeCommand message, etc.) to the UE  102  through the DU  174 , the CU  172  generates a PDCP PDU including the RRC message and generates a DL interface message (i.e., CU to DU interface message) including the PDCP PDU. The CU  172  sends the DL interface message to the UE  102 . The DU  174  extracts the PDCP PDU from the DL interface message and transmits the PDCP PDU to the UE  102  through RLC ( 206 A,  206 B), MAC ( 204 A,  204 B) and PHY ( 202 A,  202 B). In some implementations, the DL interface message is an F1 application protocol (F1AP) message, e.g., a DL RRC Message Transfer message, a UE Context Modification Request message, or a UE Context Modification Confirm message. Similarly, the UE  102  generates a PDCP PDU including a UL RRC message (e.g., the RRC reconfiguration complete message, the SecurityModeComplete message, etc.) and transmits the PDCP PDU to the DU  174  through RLC ( 206 A,  206 B), MAC ( 204 A,  204 B) and PHY ( 202 A,  202 B). When the DU  174  receives the PDCP PDU from the UE  102 , the DU  174  generates a UL interface message (i.e., DU to CU interface message) including the PDCP PDU and sends the UL interface message to the CU  172 , which in turn obtains the PDCP PDU from the UL interface message and obtains the UL RRC message from the PDCP PDU. In some implementations, the UL interface message is a F1AP message, e.g., a UL RRC Message Transfer message, a UE Context Modification Response message, or a UE Context Modification Required message. 
     In some implementations, if the base station  104 A is a gNB, the RRC reconfiguration message and the RRC reconfiguration complete message can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. In other implementations, if the base station  104 A is an eNB or an ng-eNB, the RRC reconfiguration message and the RRC reconfiguration complete message can be an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. 
     Now referring to  FIG.  3 B , according to a scenario  300 B, the base station  104 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  3 A  and  FIG.  3 B  are discussed below. 
     In contrast to event  314 A, the DU  174  determines  313 B not to generate a MeasGapConfig in response to the NeedForGapsInfo, i.e., because the DU  174  determines the UE  102  does not need gaps to perform measurements. In response to the determination  313 B, the DU  174  does not configure gaps for the UE  102  and generates a UE Context Modification Response message excluding a MeasGapConfig. The DU  174  sends  316 B the UE Context Modification Response message to the CU  172  in response to the UE Context Modification Request message  312 B. The events  312 B,  313 B and  316 B are collectively referred to in  FIG.  3 B  as a UE Context Modification procedure  360 B. 
     After the CU  172  receives  316 B the UE Context Modification Response message, the CU  172  can generate a MeasConfig which configures the UE  102  to perform measurements on a carrier frequency in a frequency band that the UE  102  does not need gaps to measure. The CU  172  sends  318 B an RRC reconfiguration message including the MeasConfig to the DU  174  which in turn transmits  320 B the RRC reconfiguration message to the UE  102 . In contrast to the event  318 A, the RRC reconfiguration message  318 B does not include a MeasGapConfig. In response to the RRC reconfiguration message, the UE  102  transmits  322 B an RRC reconfiguration complete message to the DU  174  which in turn sends  324 B the RRC reconfiguration complete message to the CU  172 . The events  318 B,  320 B,  322 B and  324 B are collectively referred to in  FIG.  3 B  as a measurement configuration procedure  380 B. 
     Now referring to  FIG.  3 C , according to a scenario  300 C, the base station  104 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  3 A  and  FIG.  3 C  are discussed below. 
     In the scenario  300 C, the CU  172  analyzes the NeedForGapsInfo and determines that the UE  102  needs gaps to perform measurements on at least one carrier frequency. In response, the CU  172  determines  311 C to request gaps for the UE  102 . In response to the determination  311 C, the CU  172  sends  312 C to the DU  174  a UE Context Modification Request message including first information, where the first information requests gaps for the UE  102 . The first information, for example, may be an information element requesting that the DU  174  generate a measurement gap configuration including measurement gaps for the UE  102 . In response, the DU  174  generates  315 C a MeasGapConfig for the UE  102  based on the first information. In some implementations, the DU  174  generates  315 C a MeasGapConfig including a GapConfig configuring gaps for the UE  102  based on the first information. In other implementations, the DU  174  generates  315 C a MeasGapConfig updating a previously configured GapConfig for the UE  102  based on the first information. 
     In some implementations, the first information includes frequency information indicating at least one carrier frequency for which the CU  172  requests the DU  174  to configure gaps, and/or includes SMTC information for the at least one carrier frequency in a UE Context Modification Request message. The DU  174  can generate a GapConfig configuring gaps for the UE  102  to measure the at least one carrier frequency and include the GapConfig in the MeasGapConfig or in the UE Context Modification Response message. In some implementations, the CU  172  can determine the first information according to the NeedForGapsInfo. For example, if the CU  172  determines that the UE  102  needs gaps to measure a particular carrier frequency of a frequency band according to the NeedForGapsInfo, the CU  172  indicates the particular carrier frequency or the frequency band in the frequency information and/or includes SMTC information for the particular carrier frequency. If the CU  172  determines that the UE  102  does not need gaps to measure a particular carrier frequency according to the NeedForGapsInfo, the CU  172  does not indicate the particular carrier frequency or the frequency band in the frequency information and/or include SMTC information for the particular carrier frequency or the frequency band. 
     In accordance with 3GPP technical specification (TS) 38.473, if the CU  172  includes SMTC information for a frequency in a UE Context Modification Request message, then the DU  174  shall generate measurement gaps based on the SMTC information. Thus, the DU  174  generates  315 C the MeasGapConfig based on the SMTC information. The DU  174  transmits  316 C to the CU  172  a UE Context Modification Response message including the MeasGapConfig. The event  311 C,  312 C,  315 C, and  316 C are collectively referred to in  FIG.  3 C  as a UE Context Modification procedure  360 C. 
     In some implementations, the DU  174  generates a GapConfig configuring gaps where one or more SS/PBCH transmissions occur on the at least one carrier frequency. The DU  174  includes the GapConfig in the MeasGapConfig so that the UE  102  can receive or detect the SS/PBCH transmissions in the gaps on the at least one carrier frequency. In one implementation, the at least one carrier frequency can include the first carrier frequency. In another implementation, the at least one carrier frequency can include the first carrier frequency and the second carrier frequency. 
     Now referring to  FIG.  3 D , according to a scenario  300 D, the base station  104 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  3 C  and  FIG.  3 D  are discussed below. 
     In contrast to the scenario  300 C, in the scenario  300 D the CU  172  analyzes the NeedForGapsInfo and determines  309 D that the UE does not need gaps to perform measurements on at least one carrier frequency as a result of analyzing the NeedForGapsInfo. In response, the CU  172  may send  312 D, to the DU  174 , a UE Context Modification Request message that does not indicate the DU  174  to configure gaps for the UE  102  or that indicates to the DU  174  to release gaps configured in a current GapConfig (i.e., previously configured) for the UE  102 . In response to the UE Context Modification Request message, the DU  174  does not configure gaps for the UE  102  or releases the GapConfig, and sends  316 D a UE Context Modification Response message to the CU  172 . In one implementation, the DU  174  generates a new MeasGapConfig indicating releasing the current GapConfig. In another implementation, the CU  172  generates a new MeasGapConfig indicating releasing the current GapConfig. In these implementations, the CU  172  can include the new MeasGapConfig in the current MeasConfig in the RRC reconfiguration message the CU  172  transmits at event  318 B. The UE  102  releases the current GapConfig in response to the new MeasGapConfig. Alternatively, the CU  172  refrains from sending a UE Context Modification Request message requesting the DU  174  to configure gaps for the UE  102  in response to the determination  309 D. The events  309 D,  312 D and  316 D are collectively referred to in  FIG.  3 D  as a UE Context Modification procedure  360 D. 
     In some implementations, the UE  102  may use gaps configured in the current GapConfig to measure a particular carrier frequency before releasing the current GapConfig. After releasing the current GapConfig, the UE  102  may measure the particular carrier frequency without using gaps. 
     In some implementations, the CU  172  indicates to the DU  174  to release gaps configured for the UE  102  or to not generate gaps for the UE  102  by excluding SMTC information in the UE Context Modification Request message transmits at event  312 A. The DU  174  releases the current GapConfig (i.e., gaps configured for the UE  102 ) or does not configure gaps for the UE  102  (e.g., does not generate a MeasGapConfig configuring gaps for the UE  102 ) in response to the UE Context Modification Request message excluding SMTC information. In other implementations, the CU  172  includes, in the UE Context Modification Request message, an indication to release gaps configured for the UE  102  or to not configure gaps for the UE  102 . For example, the indication can be a dedicated IE defined specifically to indicate that the DU  174  should not generate a measurement gap configuration. In yet other implementations, the CU  172  indicates in the UE Context Modification Request message to exclude or release (all of) the at least one carrier frequency which the UE uses the gaps (i.e., the current GapConfig) to measure. For example, the CU  172  can include in the UE Context Modification Request message a MeasConfig (or a new or similar IE) excluding or releasing (all of) the at least one carrier frequency which the UE uses the gaps to measure. The DU  174  does not configure gaps for the UE  102  or releases the current GapConfig in response to the UE Context Modification Request message or the MeasConfig IE. That is, if the DU  174  identifies that (all of) the at least one carrier frequency which the UE uses the gaps to measure is released of excluded in a MeasConfig in a UE Context Modification Request message, the DU  174  does not configure gaps for the UE  102  or releases the current GapConfig. Otherwise, the DU  174  either generates a new GapConfig configuring gaps for the UE  102 , updates the current GapConfig, or retains the current GapConfig (i.e., does not generate a new GapConfig). The DU  172  can include the new GapConfig in a MeasGapConfig and include the MeasGapConfig in the UE Context Modification Response message. The new GapConfig and the current GapConfig can be the same or different. In some implementations, the CU  172  can include a measurement object list (e.g., a MeasObjectToAddModList IE or a MeasObjectToRemoveList IE) in the MeasConfig to exclude or release the (all of) at least one carrier frequency which the UE uses the gaps to measure. For example, the CU  172  excludes the (all of) at least one carrier frequency in the MeasObjectToAddModList. In another example, the CU  172  releases the (all of) at least one carrier frequency in the MeasObjectToRemoveList. 
     In some implementations, the UE  102  generates the NeedForGapsInfo described above (i.e., with reference to  FIGS.  3 A- 3 D ) for single connectivity (SC) cases. The CU  172  or the DU  174  uses the NeedForGapsInfo described in  FIGS.  3 A- 3 D  to determine whether the UE  102  needs gaps only when the UE  102  is SC. For example, the base station  104 A determines that the UE in SC is capable of performing measurements on one or more carrier frequencies of a particular frequency band without gaps according to the NeedForGapsInfo. In response to the determination, the base station  104 A transmits a MeasConfig configuring the UE  102  in SC to measure the one or more carrier frequencies without configuring gaps to the UE  102 . Later, the base station  104 A (i.e., MN  104 A) configures the UE in DC as described below with reference to  FIG.  5 A- 5 D . The MN  104 A transmits a MeasGapConfig configuring gaps to the UE  102  which has/is being in DC so that the UE  102  in DC uses gaps configured in the MeasGapConfig to perform measurements on the one or more carrier frequencies. That is, the UE  102  in DC is not capable of performing measurements on the one or more carrier frequencies without gaps. Before receiving the MeasGapConfig, the UE  102  in DC can suspend performing measurements on the one or more carrier frequencies. The MN  104 A can include the MeasGapConfig in an RRC message (e.g., an RRC container message  542 A or an RRC reconfiguration message generated by the MN  104 A) and transmit the RRC message to the UE  102 . The UE  102  transmits an RRC response message (e.g., an RRC container response message  543 A or an RRC reconfiguration complete message generated by the UE  102 ) to the MN  104 A in response to the RRC message. The MN  104 A can release the gaps configured in the MeasGapConfig while or after the UE  102  transitions from DC to SC. In some implementations, the MN  104 A can be a disaggregated base station consisting of CU  172  and DU  174  or can be an aggregated (or integrated) base station. The UE  102  can additionally transmit a NeedForGapsInfo for DC cases to the MN  104 A or the MN  104 A can receive the NeedForGapsInfo for DC cases from another base station (e,g, base station  104 B) or the CN  110  (e.g., MME  114  or AMF  164 ). If the MN  104 A receives the NeedForGapsInfo for DC cases, the MN  104 A can determine whether the UE in DC is capable of performing measurements on one or more carrier frequencies of a particular frequency band with or without gaps according to the NeedForGapsInfo for DC cases. If the MN  104 A determines no gaps are needed, the MN  104 A does not transmit a MeasGapConfig configuring gaps to the UE  102  which has/is being in DC so that the UE  102  in DC performs measurements on the one or more carrier frequencies. 
     In other implementations, the UE  102  generates the NeedForGapsInfo described above for both SC and DC cases. The base station  104 A can use the NeedForGapsInfo as described in  FIGS.  3 A- 3 D  to determine whether the UE  102  needs gaps irrespective of the UE  102  is in SC or DC. In yet other implementations, the UE  102  can generate a NeedForGapsInfo only for the DC cases as described in  FIG.  5 A . In some implementations, the MN  104 A can be a disaggregated base station consisting of CU  172  and DU  174  or can be an aggregated (or integrated) base station. 
     Now referring to  FIG.  3 E , according to a scenario  300 E, the base station  104 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences among the scenarios of  FIG.  3 E  and  FIGS.  3 A-B  are discussed below. 
     The CU  172  may receive a UE Capability (e.g., a NeedForGapsInfo IE, an interFrequencyMeas-NoGap field, a UE-NR-Capability IE, a UE-EUTRA-Capability IE, and/or a UE-MRDC-Capability IE) of the UE  102  at event  302 E. For example, the CU  172  receives the UE Capability in an UECapabilityInformation message from the UE  102  during a UE Capability Enquiry procedure. In another example, the CU  172  can receive the UE Capability from another base station (e.g., base station  104 B) or CN  110  (not shown in  FIG.  3 E ). 
     After receiving the UE Capability, the CU  172  sends  312 E a UE Context Request message (e.g., UE Context Modification Request or UE Context Setup Request message) including the UE Capability to the DU  174 . The DU  174  can determine  314 E whether the UE needs gaps according to the UE Capability. If the DU  174  determines based on the UE Capability that the UE needs gaps for measuring a carrier frequency, the DU  174  generates a MeasGapConfig configuring gaps for the UE  102  as described for event  314 A and sends  316 E a UE Context Response message including the MeasGapConfig. If the DU  174  determines based on the UE Capability that the UE does not need gaps, the DU  174  does not generate a GapConfig for the UE  102  and sends  316 E a UE Context Response message excluding a GapConfig, or alternatively, the DU  174  generates a MeasGapConfig releasing a GapConfig previously configured for the UE  102  and sends  316 E a UE Context Response message including the MeasGapConfig. The events  312 E,  314 E, and  316 E are collectively referred to in  FIG.  3 E  as a UE Context procedure  360 E. 
     Before or after receiving the UE Context Response message, the CU  172  can generate  342 E a first configuration enabling the UE  102  to perform inter-frequency measurement on reference signal(s) (RS(s)) within an active DL BWP without measurement gaps. The RS(s) can be channel state information RS(s) (CSI-RS(s)) or synchronization signal and/or physical broadcast channel (PBCH) block (SSB). In some implementations, if the UE Capability includes the interFrequencyMeas-NoGap field, the CU  172  can generate  342 E the first configuration. In other implementations, if the UE Capability does not include the interFrequencyMeas-NoGap field, the CU  172  does not generate  342 E the first configuration. Alternatively, the CU  172  may not generate the first configuration and may instead receive  342 E the first configuration from the DU  174  in the UE Context Response message at event  316 E. In some implementations, if the UE Capability includes the interFrequencyMeas-NoGap field, the DU  174  can generate the first configuration. In other implementations, if the UE Capability does not include the interFrequencyMeas-NoGap field, the DU  174  does not generate  342 E the first configuration. 
     If the CU  172  generates or receives the first configuration, and/or receives the MeasGapConfig, the CU  172  generates a MeasConfig including the first configuration and/or the MeasGapConfig. The CU  172  performs a measurement configuration procedure  380 B to send the MeasConfig to the UE  102 . If the MeasConfig includes the GapConfig and the UE  102  needs gaps to measure a carrier frequency (i.e., measure RS(s) on the carrier frequency), the UE  102  may use gaps configured in the GapConfig to measure the carrier frequency. If the MeasConfig includes the GapConfig and the UE  102  does not need gaps to measure a carrier frequency (i.e., measure RS(s) on the carrier frequency), the UE  102  may measure the carrier frequency with or without gaps. If the MeasConfig excludes a GapConfig or releases a GapConfig previously configured to the UE  102  and the UE  102  does not need gaps to measure a carrier frequency (i.e., measure RS(s) on the carrier frequency), the UE  102  may measure the carrier frequency without gaps. 
     In some implementations, the CU  172  can include the first information in the UE Context Request message as described for event  312 C. The DU  174  can determine whether the UE  102  needs gaps according to the first information and the UE Capability. In some implementations, if the UE Capability indicates that the UE  102  needs gaps to measure a carrier frequency in the frequency information in the first information, the DU  174  determines that the UE  102  needs gaps to measure the carrier frequency. If the UE Capability indicates that the UE  102  does not need gaps to measure all of carrier frequency(ies) in the frequency information, the DU  174  determines the UE  102  does not need gaps. 
     In other implementations, if the UE Capability does not include an interFrequencyMeas-NoGap field or the frequency information indicates that frequency location(s) of the RS(s) are not within an active DL BWP of the UE  102 , the DU  174  determines that the UE  102  needs gaps to measure the carrier frequency. If the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are within an active DL BWP of the UE  102 , the DU  174  determines that the UE  102  does not need gaps. Alternatively, if the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are within all DL BWP(s) (which can be active and/or inactive) of the UE  102 , the DU  174  determines that the UE  102  does not need gaps. If the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are not within one of all DL BWP(s) (which can be active and/or inactive) of the UE  102 , the DU  174  determines that the UE  102  need gaps. 
     In some implementations, the DU  174  may still generate a MeasGapConfig configuring gaps according to the SMTC information of a carrier frequency in the first information, even though the UE Capability indicates that the UE  102  does not need gaps. The DU  174  determines locations of gaps to align with the location of the RS(s) in time domain as much as possible, so that the UE  102  can quickly search, receive, identity or measure the RS(s) according to the gaps. In one implementation, the time location of the RS(s) and the time location of the gaps can partially or complete overlap. In another implementation, the time location of the RS(s) are close to the time location of the gaps. 
     Next referring to  FIG.  3 F , according to a scenario  300 F, the base station  104 A includes a CU  172  and a DU  174  and provides communication services to the UE  102 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences among the scenarios of  FIG.  3 F  and  FIGS.  3 C-E  are discussed below. 
     In contrast to the  FIG.  3 E , the CU  172  determines  313 F whether the UE  102  needs gaps according to the UE Capability. If the CU  172  determines the UE  102  needs gaps, the CU  172  can send  312 F a UE Context Request message (e.g., a UE Context Setup Request or UE Context Setup Response message) to the DU  174 , similar to event  312 C. In response, the DU  174  sends  316 F a UE Context Response message including the MeasGapConfig configuring gaps for the UE  102  to the CU  172 , similar to the event  316 C. If the CU  172  determines that the UE  102  does not need gaps, the CU  172  can send  312 F a UE Context Request message (e.g., a UE Context Setup Request or UE Context Setup Response message) to the DU  174 , similar to event  312 D. In response, the DU  174  sends  316 F a UE Context Response message including the MeasGapConfig configuring gaps for the UE  102  to the CU  172 , similar to the event  316 D. The events  313 F,  312 F, and  316 F are collectively referred to in  FIG.  3 F  as a UE Context procedure  360 F. 
     In some implementations, the CU  172  can determine whether the UE  102  needs gaps according to the first information and the UE Capability. In some implementations, if the UE Capability indicates that the UE  102  needs gaps to measure a carrier frequency in the frequency information in the first information, the CU  172  determines the UE  102  needs gaps to measure the carrier frequency. If the UE Capability indicates that the UE  102  does not need gaps to measure all of carrier frequency(ies) in the frequency information, the CU  172  determines the UE  102  does not need gaps. 
     In other implementations, if the UE Capability does not include an interFrequencyMeas-NoGap field or the frequency information indicates frequency location(s) of the RS(s) are not within an active DL BWP of the UE  102 , the CU  172  determines that the UE  102  needs gaps to measure the carrier frequency. If the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are within an active DL BWP of the UE  102 , the CU  172  determines that the UE  102  does not need gaps. Alternatively, if the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are within all DL BWP(s) (which can be active and/or inactive) of the UE  102 , the CU  172  determines that the UE  102  does not need gaps. If the UE Capability includes an interFrequencyMeas-NoGap field and the frequency information indicates that frequency location(s) of the RS(s) are not within one of all DL BWP(s) (which can be active and/or inactive) of the UE  102 , the CU  172  determines that the UE  102  need gaps. 
     In some implementations, the CU  174  may still send the UE Context Request message to the DU  174  to request that the DU  172  configure gaps for the UE  102 , even though the UE Capability indicates that the UE  102  does not need gaps. In response to the UE Context Request message, the DU  174  determines locations of gaps to align with location of the RS(s) in time domain as much as possible. Therefore, the UE  102  can quickly search, receive, identity or measure the RS(s) according to the gaps. 
     In  FIG.  3    (i.e., any one of  FIGS.  3 A- 3 F ), the DU  174  in some implementations does not include the MeasGapConfig in the UE Context Response message. Instead, the DU  174  sends a UE Context Modification Required message including the MeasGapConfig to the CU  172  and the CU  172  sends a UE Context Modification Confirm message to the DU  174  in response. In  FIG.  3   , the CU  172  in some implementations may send the first information and the UE Capability in different UE Context Request messages to the DU  174 . In response to each of the different UE Context Request messages, the DU  174  sends a UE Context Response message to the CU  172 . In  FIG.  3   , the DU  172  may or may not include a DU configuration in the UE Context Response message. The UE Context procedure (e.g., UE Context Setup procedure or UE Context Modification procedure)  360 E or  360 F can apply to  FIG.  4    (e.g., any one of  FIGS.  4 B- 4 I ),  FIG.  5    (e.g., any one of  FIGS.  5 C- 5 D ) or  FIG.  6    (e.g.,  FIG.  6 A- 6 B ) below. 
       FIGS.  3 A- 3 F  depict measurement gap configuration techniques that the base station  104 A can implement.  FIGS.  4 A- 4 I  depict handover scenarios in which one or more base station(s) can implement the techniques discussed above. More particularly,  FIGS.  4 A- 4 E  depict techniques for managing measurement gap configurations involving handover from a source base station (S-BS) to a target base station (T-BS), and  FIGS.  4 F- 4 I  depict using similar techniques in scenarios involving handover within a distributed base station (e.g., handover from a source DU (S-DU) to a target DU (T-DU)). 
     Now referring to  FIG.  4 A , a scenario  400 A involves a handover scenario. In this scenario, the base station  104 A operates as a source base station (S-BS), and the base station  104 B operates as a target base station (T-BS). 
     Initially, the UE  102  communicates  402 A data (e.g., uplink (UL) data PDUs and/or downlink (DL) data PDUs) with the S-BS  104 A using an S-BS configuration. In some scenarios, the UE  102  communicates  402 A data in SC with the S-BS  104 A, or communicates  402 A data in DC with the S-BS  104 A operating as an MN and an SN (e.g., the base station  106 A) not shown in  FIG.  4 A . Then, the S-BS  104 A initiates an RRC reconfiguration procedure with the UE  102  by sending  404 A an RRC reconfiguration including a first NeedForGapsConfig to the UE  102 , similar to events  304 A and  306 A. In response to the first NeedForGapsConfig, the UE  102  includes a first NeedForGapsInfo in an RRC reconfiguration complete message. The UE  102  transmits  408 A the RRC reconfiguration message including the first NeedForGapsInfo to the S-BS  104 A, similar to events  308 A and  310 A. The events  406 A and  408 A are collectively referred to in  FIG.  4 A  as a need for gap information procedure  450 A. 
     Later in time, the S-BS  104 A determines  407 A to initiate handover for the T-BS  104 B and the UE  102  to communicate, e.g., blindly or in response to detecting a suitable event. For example, the determination  407 A can occur in response to the S-BS  104 A receiving one or more measurement results from the UE  102  that are above (or below) one or more predetermined thresholds, or calculating a filtered result (from the measurement result(s)) that is above (or below) a predetermined threshold. In another example, the suitable event can be that the UE  102  is moving toward the T-BS  104 B. In yet another example, the suitable event can be one or more measurement results, generated or obtained by the S-BS  104 A based on measurements of signals received from the UE  102 , being above (or below) one or more predetermined thresholds. 
     After determining  407 A to initiate handover, the S-BS  104 A sends  471 A a Handover Request message including the S-BS configuration and the first NeedForGapsInfo to the T-BS  104 B. In response to the Handover Request message, the T-BS  104 B determines  414 A to include or exclude a MeasGapConfig in a handover command according to the first NeedForGapsInfo, similar to the determination made by the CU  172  or the DU  174  in events  314 A,  313 B,  311 C, or  309 D. If the T-BS  104 B determines to include a first MeasGapConfig according to the first NeedForGapsInfo, the T-BS  104 B can include the first MeasGapConfig in a first MeasConfig and include the first MeasConfig in the handover command message, in one implementation. In another implementation, the T-BS  104 B can include the first MeasConfig in an RRC reconfiguration message, as discussed below with reference to event  420 A. 
     The T-BS  104 B includes the handover command message in a Handover Request Acknowledge message and sends  472 A the Handover Request Acknowledge message to the S-BS  104 A in response to the Handover Request message. In turn, the S-BS  104 A transmits  474 A the handover command message to the UE  102 . The handover command message can include one or more random access configurations needed by the UE  102  to handover to the T-BS  104 B, and in some implementations, includes additional fields, such as a mobility field (e.g., mobilityControlInfo field or a reconfigurationWithSync field), which can include some or all of the random access configurations. The handover command message can also include multiple configuration parameters. The multiple configuration parameters can configure zero, one, or more radio bearers, including SRB(s) and/or DRB(s). The multiple configuration parameters can also configure zero, one or more SCells, configure PCell  124 B, and/or configure a physical layer configuration, a MAC configuration, and an RLC configuration. 
     In attempting to perform the handover, the UE  102  initiates  475 A a random access procedure with the T-BS  104 B via a target cell (e.g., PCell  124 B) covered by the T-BS  104 B, e.g., using one or more random access configurations in the handover command message received  472 A from the S-BS  104 A. After gaining access to a channel, the UE  102  transmits  477 A a handover complete message to the T-BS  104 B via the target cell during or after successfully completing the random access procedure. After the UE  102  successfully completes the random access procedure (i.e., the T-BS  104 B identifies the UE  102  during the random access procedure), the UE  102  communicates  479 A control signals and data (e.g., UL data PDUs or DL data PDUs) with the T-BS  104 B via the target cell using configurations in the handover command message. 
     In implementations where the T-BS  104 B does not include the first MeasConfig in the handover command at event  472 A, after receiving  477 A the handover complete message, the T-BS  104 B can transmit  420 A an RRC reconfiguration message including the first MeasConfig to the UE  102 . In response, the UE  102  transmits  422 A an RRC reconfiguration complete message to the T-BS  104 B. The first MeasConfig configures the UE  102  to measure at least one carrier frequency. If the T-BS  104 B included the first MeasConfig in the handover command message at event  472 A, then events  420 A and  422 A may not be needed or alternatively the T-BS  104 B can include another MeasConfig configuring the UE  102  to measure an additional carrier frequency in the RRC reconfiguration message at event  420 A. If the first MeasGapConfig configures gaps, the UE  102  may perform measurements on the additional carrier frequency by using gaps configured in the first MeasGapConfig. Otherwise, the UE  102  may perform measurements on the additional carrier frequency without gaps. 
     If the first MeasGapConfig transmitted in the handover command message (at  472 A- 474 A) or the RRC reconfiguration message (at  420 A) includes a GapConfig, the UE  102  can perform measurements on at least one carrier frequency using gaps in the GapConfig. If the first MeasGapConfig is not included in the handover command message or the RRC reconfiguration message, the UE  102  can perform measurements on the at least one carrier frequency without gaps. If the first MeasGapConfig releases a GapConfig which was configured by the S-BS  104 A, the UE  102  can perform measurements on the at least one carrier frequency without gaps. The UE  102  obtains a measurement result from the measurements and transmits  426 A a measurement report message including the measurement result to the T-BS  104 B. For example, the measurement result can indicate a value of a reference signal received power (RSRP), reference signal received quality (RSRQ), Received Signal Strength Indicator (RSSI), or signal to noise and interference ratio (SINR) and/or indicate a reporting event. According to the measurement result, the T-BS  104 B can decide whether to configure an SCell to the UE  102  or handover the UE  102  to another cell. For example, if the measurement result associated with a cell is above a predetermined threshold, the T-BS  104 B can configure the cell as an SCell to the UE  102 . In another example, if the measurement result associated with a cell is above a predetermined threshold, the T-BS  104 B can configure the UE  102  to handover to the cell. 
     After the handover, the T-BS  104 B can transmit to the UE  102  a first RRC reconfiguration message including a second NeedForGapsConfig which indicates one or more additional frequency bands, in some implementations. The UE  102  indicates whether gaps are needed to perform measurements for the one or more additional frequency bands in a second NeedForGapsInfo, and includes the second NeedForGapsInfo in a first RRC reconfiguration complete message and transmits the first RRC reconfiguration complete message to the T-BS  104 B in response to the first RRC reconfiguration message. Based on the second NeedForGapsInfo, the T-BS  104 B can determine whether to generate a MeasGapConfig configuring gaps for the UE  102  to measure a carrier frequency in the one or more additional frequency bands. If the T-BS  104 B determines the UE  102  needs gaps to measure a carrier frequency in the one or more additional frequency bands, the T-BS  104 B generates a second MeasGapConfig configuring gaps. 
     The T-BS  104 B can transmit a second RRC reconfiguration message including a second MeasConfig to the UE  102 , wherein the second MeasConfig can configure a particular carrier frequency in one of the one or more additional carrier frequency bands. The UE  102  transmits a second RRC reconfiguration complete message to the T-BS  104 B in response to the second RRC reconfiguration message. In one implementation, the T-BS  104 B can include the second MeasGapConfig in the second MeasConfig or the second RRC reconfiguration message. In another implementation, the T-BS  104 B does not include the second MeasGapConfig in the second RRC reconfiguration message. In this implementation, the T-BS  104 B can transmit a third RRC reconfiguration message including the second MeasGapConfig to the UE  102  and in response, the UE  102  transmits a third RRC reconfiguration complete message to the T-BS  104 B. Thus, the UE  102  can use the gaps in the second MeasGapConfig to perform measurements on the particular carrier frequency. If the T-BS  104 B determines the UE  102  does not need gaps to measure the particular carrier frequency based on the second NeedForGapsInfo, the T-BS  104 B does not generate a MeasGapConfig for the UE  102  to measure the particular carrier frequency. The UE  102  performs measurements on the particular carrier frequency without using gaps. The UE  102  obtains a measurement result from the measurements and transmits a measurement report message to the T-BS  104 B. The T-BS  104 B can transmit the second RRC reconfiguration message before or after the third RRC reconfiguration message. 
     In some implementations, the S-BS  104 A can include the first NeedForGapsConfig (transmitted to the UE  102  at event  406 A) in the Handover Request message the S-BS  104 A transmits  471 A to the T-BS  104 B. Based on the NeedForGapsConfig, the T-BS  104 B can determine the frequency bands for which the S-BS  104 A requested measurement gap capability information. 
     In some implementations, if the S-BS  104 A is a gNB, the RRC reconfiguration message  406 A and the RRC reconfiguration complete  408 A message can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. In other implementations, if the S-BS  104 A is an eNB or an ng-eNB, the RRC reconfiguration message  406 A and the RRC reconfiguration complete message  408 A can be an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. 
     In some implementations, if the T-BS  104 B is a gNB, the RRC reconfiguration message and the RRC reconfiguration complete message exchanged between the UE  102  and the T-BS  104 B can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. In some implementations, if the T-BS  104 B is an eNB or an ng-eNB, the RRC reconfiguration message and the RRC reconfiguration complete message exchanged between the UE  102  and the T-BS  104 B can he an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. 
     In some implementations, if the T-BS  104 B is a gNB. the handover command message and the handover complete message can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. If the S-BS  104 A is an eNB or ng-eNB, the S-BS  104 A can include the RRCReconfiguration in a MobilityFromEUTRACommand message and transmits  474  the MobilityFromEUTRACommand message to the UE  102 . In some implementations, if the T-BS  104 B is an eNB or an ng-eNB, the handover command message and the handover complete message can be an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. If the S-BS  104 A is an gNB, the S-BS  104 A can include the RRCConnectionReconfiguration in a MobilityFromNRCommand message and transmits  474  the MobilityFromNRCommand message to the UE  102 . 
     Although the S-BS  104 A and the T-BS  104 B are interconnected via an X2 or Xn interface in the example systems of  FIGS.  1 A and  1 B , in other scenarios the S-BS  104 A and the T-BS  104 B may not have an interface (i.e., an X2 or Xn interface). In these cases, the S-BS  104 A can transmit a Handover Required message including the S-BS configuration and the NeedForGapsInfo to the CN  110  (e.g., MME  114  or AMF  164 ) instead of transmitting  471 A the Handover Request message. The CN  110  includes the S-BS configuration and the NeedForGapsInfo in a Handover Request message generated by the CN  110  as described for the Handover Request message  471 A. The CN  110  sends the generated Handover Request message to the T-BS  104 B. That is, the Handover Required message and the CN generated Handover Request message can be used instead of the Handover Request message  471 A. The T-BS  104 B generates a Handover Request Acknowledge message which includes the handover command message, and sends the Handover Request Acknowledge message to the CN  110  in response to the Handover Request message received from the CN  110 . The CN  110  sends a Handover Confirm message including the handover command message to the S-BS  104 A in response to the Handover Required message. That is, the Handover Request Acknowledge message and the CN generated Handover Confirm message can be used instead of the Handover Request Acknowledge message  472 A. 
     Now referring to  FIG.  4 B , a scenario  400 B involves a handover scenario. In this scenario, the base station  104 A operates as a source base station (S-BS), and the base station  104 B operates as a target base station (T-BS) consisting of a T-CU  172  and a T-DU  174 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIGS.  4 A and  4 B  are discussed below. 
     In the scenario  400 B, the S-BS  104 A sends  471 B a Handover Request message including the S-BS configuration and the first NeedForGapsInfo to the T-CU  172 . In response to the Handover Request message, the T-CU  172  sends  412 B a UE Context Setup Request message including the first NeedForGapsInfo to the T-DU  174  for the UE  102 . The T-DU  174  generates  414 B a first MeasGapConfig in response to the first NeedForGapsInfo. The T-DU  174  also generates a T-DU configuration in response to the UE Context Setup Request message. In some implementations, the T-DU  174  can configure gaps in a GapConfig and includes the GapConfig in the first MeasGapConfig because the T-DU  174  determines the UE  102  needs gaps to perform measurements. In other implementations, the T-DU  174  can release a GapConfig which was configured to the UE  102  at event  402 B because the T-DU  174  determines the UE  102  does not need the GapConfig to perform measurements. 
     The T-CU  172  can include the S-BS configuration in the UE Context Setup Request message. In some implementations, the T-DU  174  generates the T-DU configuration as a full T-DU configuration (i.e., a complete and self-contained configuration). In other implementations, the T-DU  174  generates the T-DU configuration as a delta T-DU configuration which augments a portion of the S-BS configuration. The T-DU configuration can include one or more random access configurations needed by the UE  102  to handover to the T-DU  174 , and in some implementations, includes additional fields, such as a mobility field (e.g., mobilityControlInfo field or a reconfigurationWithSync field), which can include some or all of the random access configurations. The T-DU configuration can also include multiple configuration parameters. The multiple configuration parameters can configure PCell  124 B, and/or configure a physical layer configuration, a MAC configuration, and an RLC configuration. 
     In response to the UE Context Setup Request message, the T-DU  174  sends  416 B a UE Context Setup Response message including the T-DU configuration and the first MeasGapConfig to the T-CU  172 . The events  412 B,  414 B, and  416 B are collectively referred to in  FIG.  4 B  as a UE Context Setup procedure  460 B. The UE Context Setup procedure  460 B is generally similar to the UE Context Modification procedure  360 A, except that the messages exchanged in procedure  460 B are UE Context Setup messages rather than UE Context Modification messages. 
     In response to the UE Context Setup Response message, the T-CU  172  generates a handover command message that includes the T-DU configuration and the first MeasGapConfig, and includes the handover command message in a Handover Request Acknowledge message. In one implementation, the T-CU  172  can include the first MeasGapConfig in a first MeasConfig in the handover command message. The T-CU  172  sends  472 B the Handover Request Acknowledge message to the S-BS  104 A in response to the Handover Request message. In turn, the S-BS  104 A transmits  474 B the handover command message to the UE  102 . In response to the handover command message, the UE  102  performs  475 B a random access procedure with the T-DU  174 , e.g., using one or more random access configurations in the T-DU configuration. The UE  102  transmits  477 B a handover complete message to the T-DU  174  during or after successfully completing the random access procedure, which in turn sends  478 B the handover complete message to the T-CU  172 . After the T-DU  174  identifies the UE  102  during the random access configuration (e.g., the UE  102  succeeds in the contention resolution during the random access procedure), the UE  102  communicates  479 B control signals and data with the T-DU  174  using the T-DU configuration and communicates  479 B control messages and data with the T-CU  172  via the T-DU  174 . 
     After receiving the handover complete message, the T-CU  172  can send  418 B an RRC reconfiguration message including a first MeasConfig to the T-DU  174 . The T-DU  174  in turn transmits  420 B the RRC reconfiguration message to the UE  102 . In response, the UE  102  transmits  422 B an RRC reconfiguration complete message to the T-DU  174 , which in turn sends  424 B sends the RRC reconfiguration complete message to the T-CU  172 . The events  418 B,  420 B,  422 B and  424 B are collectively referred to in  FIG.  4 B  as a measurement configuration procedure  480 B. The T-CU  172  can include the first MeasGapConfig in the first MeasConfig in the RRC reconfiguration message instead of the handover command message. The first MeasConfig in the RRC reconfiguration message can configure the UE  102  to measure at least one carrier frequency. If the first MeasConfig in the handover command configures the UE  102  to measure the at least one carrier frequency, the measurement configuration procedure  480 B may not be needed or alternatively the T-CU  172  can include another MeasConfig configuring the UE  102  to measure an additional carrier frequency in the RRC reconfiguration message at event  418 A. If the first MeasGapConfig configures gaps, the UE  102  may perform measurements on the additional carrier frequency by using gaps configured in the first MeasGapConfig. Otherwise, the UE  102  may perform measurements on the additional carrier frequency without gaps. 
     The UE  102  can perform measurements on the at least one carrier frequency using the GapConfig in the first MeasGapConfig. The UE  102  obtains a measurement result from the measurements and transmits  426 B a measurement report message including the measurement result to the T-CU  174 , which in turn transmits  428 B the measurement report message to the T-CU  172 . For example, the measurement result can indicate a value of a reference signal received power (RSRP), reference signal received quality (RSRQ), Received Signal Strength Indicator (RSSI), or signal to noise and interference ratio (SINR) and/or indicate a reporting event. According to the measurement result, the T-CU  172  can decide whether to configure an SCell to the UE  102  or handover the UE  102  to another cell. For example, if the measurement result associated with a cell is above a predetermined threshold, the T-CU  172  can configure the cell as an SCell to the UE  102 . In another example, if the measurement result associated with a cell is above a predetermined threshold, the T-CU  172  can configure the UE  102  to handover to the cell. The events  426 B and  428 B are collectively referred to in  FIG.  4 B  as a measurement reporting procedure  490 B. 
     To transmit a DL RRC message (e.g., the RRC reconfiguration message, etc.) to the UE  102  through the T-DU  174 , the T-CU  172  generates a PDCP PDU including the RRC message and generates an DL interface message (i.e., CU to DU interface message) including the PDCP PDU. The T-CU  172  sends the DL interface message to the UE  102 . The T-DU  174  extracts the PDCP PDU from the DL interface message and transmits the PDCP PDU to the UE  102  through RLC ( 206 A,  206 B), MAC ( 204 A,  204 B) and PHY ( 202 A,  202 B). In some implementations, the DL interface message is an F1 application protocol (F1AP) message, e.g., a DL RRC Message Transfer message, UE Context Setup Request message, UE Context Modification Request message, or UE Context Modification Confirm message. Similarly, the UE  102  generates a PDCP PDU including a UL RRC message (e.g., the RRC reconfiguration complete message, the handover complete message, etc.) and transmits the PDCP PDU to the T-DU  174  through RLC ( 206 A,  206 B), MAC ( 204 A,  204 B) and PHY ( 202 A,  202 B). When the T-DU  174  receives the PDCP PDU from the UE  102 , the T-DU  174  generates an UL interface message (i.e., DU to CU interface message) including the PDCP PDU and sends the UL interface message to the T-CU  172 , which in turn obtains the PDCP PDU from the UL interface message and obtains the UL RRC message from the PDCP PDU. In some implementations, the UL interface message is a F1AP message, e.g., an Initial UL RRC Message Transfer message, UL RRC Message Transfer message, UE Context Setup Response message, UE Context Modification Response message, or UE Context Modification Required message. 
     After the handover, the T-CU  172  can generate a first RRC reconfiguration message including a second NeedForGapsConfig which indicates one or more additional frequency band, in some implementations. The T-CU  172  sends the first RRC reconfiguration message to the T-DU  174  which in turn transmits the first RRC reconfiguration message to the UE  102 . The UE  102  indicates whether gaps are needed to perform measurements for the one or more additional frequency bands in a second NeedForGapsInfo, includes the second NeedForGapsInfo in a first RRC reconfiguration complete message, and transmits the first RRC reconfiguration complete message to the T-DU  174  in response to the first RRC reconfiguration message. The T-DU  174  in turn sends the first RRC reconfiguration complete message to the T-CU  172 . The T-CU  172  may perform a UE Context Modification procedure similar to event  360 A,  360 B,  360 C or  360 D with the T-DU  174 . If the T-CU  172  receives a second MeasGapConfig from the T-DU  174  in the UE Context Modification procedure, the T-CU  172  can include the second MeasGapConfig in a second MeasConfig. The T-CU  172  can transmit a second RRC reconfiguration message including the second MeasConfig to the UE  102 . The UE  102  transmits a second RRC reconfiguration complete message to the T-DU  174  in response to the second RRC reconfiguration message. The T-DU  174  in turn sends the second RRC reconfiguration complete message to the T-CU  172 . In one implementation, the T-CU  172  can configure the UE  102  to measure a particular carrier frequency in one of the one or more additional carrier frequency bands in the second MeasConfig. In another implementation, the T-CU  172  can send a third RRC reconfiguration message including a third MeasConfig to the T-DU  174 , wherein the third MeasConfig configures the UE  102  to measure the particular carrier frequency. The DU  174  in turn transmits the third RRC reconfiguration message to the UE  102 . The UE  102  transmits a third RRC reconfiguration complete message to the T-DU  174  in response to the third RRC reconfiguration message. The T-DU  174  in turn sends the third RRC reconfiguration complete message to the T-CU  172 . If the second MeasGapConfig configures gaps, the UE  102  can use the gaps in the second MeasGapConfig to perform measurements on the particular carrier frequency. Otherwise, the UE  102  performs measurements on the particular carrier frequency without using a gap. The UE  102  obtains a measurement result from the measurements and transmits a measurement report message to the T-BS  104 B. 
     In some implementations, the S-BS  104 A can include the first NeedForGapsConfig (transmitted to the UE during a need for gap information procedure  450 B) in the Handover Request message the S-BS  104 A transmits  471 B to the T-CU  172 . Based on the NeedForGapsConfig, the T-CU  172  can determine the frequency bands for which the S-BS  104 A requested measurement gap capability information. 
     Although the S-BS  104 A and the T-CU  172  are interconnected via an X2 or Xn interface in the example systems of  FIGS.  1 A and  1 B , in other scenarios the S-BS  104 A and the T-CU  172  may not have an interface (i.e., an X2 or Xn interface). In these cases, the S-BS  104 A can transmit a Handover Required message including the S-BS configuration and the NeedForGapsInfo to the CN  110  (e.g., MME  114  or AMF  164 ) instead of transmitting  471 B the Handover Request message. The CN  110  includes the S-BS configuration and the NeedForGapsInfo in a Handover Request message generated by the CN  110  as described for the Handover Request message  471 B. The CN  110  sends the generated Handover Request message to the T-CU  172 . That is, the Handover Required message and the CN generated Handover Request message can be used instead of the Handover Request message  471 B. The T-CU  172  generates a Handover Request Acknowledge message which includes the handover command message, and sends the Handover Request Acknowledge message to the CN  110  in response to the Handover Request message received from the CN  110 . The CN  110  sends a Handover Confirm message including the handover command message to the S-BS  104 A in response to the Handover Required message. That is, the Handover Request Acknowledge message and the CN generated Handover Confirm message can be used instead of the Handover Request Acknowledge message  472 B. 
     Now referring to  FIG.  4 C , a scenario  400 C involves a handover scenario. In this scenario, the base station  104 A operates as a source base station (S-BS), and the base station  104 B operates as a target base station (T-BS). Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  4 C  and  FIGS.  4 A- 4 B  are discussed below. 
     In contrast to event  414 B, the T-DU  174  determines  413 C not to generate a MeasGapConfig in response to the first NeedForGapsInfo, i.e., because the T-DU  174  determines the UE  102  does not need gaps to perform measurements. In response to the determination  413 C, the T-DU  174  does not configure gaps for the UE  102  and generates a UE Context Setup Response message excluding a MeasGapConfig. The T-DU  174  includes a T-DU configuration in the UE Context Setup Response message. The T-DU  174  sends  416 C the UE Context Setup Response message to the T-CU  172  in response to the UE Context Setup Request message  412 C. The events  412 C,  413 C and  416 C are collectively referred to in  FIG.  4 C  as a UE Context Setup procedure  460 C. The UE Context Setup procedure  460 C is generally similar to the UE Context Modification procedure  360 B, except that the messages exchanged in the procedure  460 C are UE Context Setup messages rather than UE Context Modification messages. 
     In response to the UE Context Setup Response message, the T-CU  172  generates a handover command message that includes the T-DU configuration, and includes the handover command message in a Handover Request Acknowledge message. The T-CU  172  sends  472 C the Handover Request Acknowledge message to the S-BS  104 A in response to the Handover Request message. 
     As described for  FIG.  4 B , the T-CU  172  can include the first MeasConfig in the handover command message or in the RRC reconfiguration message. The first MeasConfig can configure the UE  102  to measure at least one carrier frequency. In contrast to  FIG.  4 B , the T-CU  172  neither includes a MeasGapConfig in the handover command message nor in the RRC reconfiguration message in the measurement configuration procedure  480 B because the T-DU  174  does not generate a MeasGapConfig at  413 C. The UE  102  can perform measurements on the at least one carrier frequency without gaps. 
     Now referring to  FIG.  4 D , a scenario  400 D involves a handover scenario. In this scenario, the base station  104 A operates as a source base station (S-BS), and the base station  104 B operates as a target base station (T-BS) consisting of a T-CU  172  and a T-DU  174 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  4 D  and  FIGS.  4 A- 4 C  are discussed below. 
     In the scenario  400 D, the S-BS  104 A sends  471 D a Handover Request message including the S-BS configuration and the first NeedForGapsInfo to the T-CU  172 . The T-CU  172  analyzes the NeedForGapsInfo and determines that the UE  102  needs gaps to perform measurements on at least one carrier frequency. In response, the T-CU  172  determines  411 D to request gaps for the UE  102  according to the NeedForGapsInfo. In response to the determination  411 D, the T-CU  172  sends  412 D the UE Context Setup Request message including the first information requesting gaps for the UE  102  to the T-DU  174 . In response, the DU  174  generates  415 D a MeasGapConfig configuring gaps for the UE  102  based on the first information. The T-DU  174  transmits  416 D a UE Context Modification Response message including the MeasGapConfig to the T-CU  172 . The T-CU  172  also can include T-DU configuration in the UE Context Setup Response message. The events  411 D,  412 D,  415 D, and  416 D are collectively referred to in  FIG.  4 D  as a UE Context Setup procedure  460 D. The UE Context Setup procedure  460 D is generally similar to the UE Context Modification procedure  360 C, except that the messages exchanged in the procedure  460 D are UE Context Setup messages rather than UE Context Modification messages. 
     After the UE Context Setup procedure  460 D, the scenario  400 D proceeds in a similar manner as the scenario  400 B after the UE Context Setup procedure  460 B. In response to the UE Context Setup Response message, the T-CU  172  generates a handover command message that includes the T-DU Configuration, and includes the handover command message in a Handover Request Acknowledge message. The T-CU  172  sends  472 D the Handover Request Acknowledge message to the S-BS  104 A in response to the Handover Request message. 
     As described for  FIG.  4 B , the T-CU  172  can include the MeasGapConfig in a MeasConfig and include the MeasConfig in either the handover command (transmitted at the event  472 D) or an RRC Reconfiguration message (transmitted during the measurement configuration procedure  480 D). 
     Now referring to  FIG.  4 E , a scenario  400 E involves a handover scenario. In this scenario, the base station  104 A operates as a source base station (S-BS), and the base station  104 B operates as a target base station (T-BS) consisting of a T-CU  172  and a T-DU  174 . Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  4 E  and  FIG.  4 D  are discussed below. 
     In contrast to the scenario  400 D, in the scenario  400 E the T-CU  172  analyzes the NeedForGapsInfo and determines  409 E that the UE does not need gaps to perform measurements on at least one carrier frequency as a result of analyzing the NeedForGapsInfo. In response, the T-CU  172  does not request the DU  174  to configure gaps for the UE  102  or indicates the DU  174  to release the configured gaps for the UE  102 . The T-CU  172  sends, to the T-DU  174 ,  412 E the UE Context Setup Request message that does not indicate to the T-DU  174  to configure gaps for the UE  102  or that indicates the T-DU  174  is to release gaps configured in a current GapConfig (previously configured) for the UE  102 . In response to the UE Context Setup Request message, the DU  174  does not configure gaps for the UE  102  or releases the current GapConfig, and send  416 E a UE Context Modification Response message to the CU  172 . In one implementation, the T-DU  174  generates a new MeasGapConfig indicating releasing the current GapConfig. In another implementation, the T-CU  172  generates a new MeasGapConfig indicating releasing the current GapConfig. In these implementations, the T-CU  172  can include the new MeasGapConfig in the MeasConfig in the handover command message  472 E. The UE  102  releases the current GapConfig in response to the new MeasGapConfig. Alternatively, the CU  172  refrains from sending a UE Context Modification Request message requesting the DU  174  to configure gaps for the UE  102  in response to the determination  409 E. The events  409 E,  412 E, and  416 E are collectively referred to in  FIG.  4 E  as a UE Context Setup procedure  460 E. 
     The UE Context Setup procedure  460 E is generally similar to the UE Context Modification procedure  360 D, except that the messages exchanged in procedure  460 E are UE Context Setup messages rather than UE Context Modification messages. After the UE Context Setup procedure  460 E, the scenario  400 E proceeds in a similar manner as the scenario  400 C after the UE Context Setup procedure  460 C. The T-CU  172  does not include a MeasGapConfig in a handover command (transmitted at event  472 E) or an RRC Reconfiguration message (transmitted during measurement configuration procedure  480 E), because the T-DU  174  does not generate a MeasGapConfig. 
       FIGS.  4 F- 4 I  depict techniques for managing measurement gap configurations involving handover within a distributed base station (e.g., handover from a source DU (S-DU) to a target DU (T-DU).  FIGS.  4 F- 4 I  depict similar techniques as  FIGS.  4 B- 4 E , respectively, except that the  FIGS.  4 F- 4 I  involve handover within a distributed base station rather than from a source base station to a target base station. 
     Now referring to  FIG.  4 F , a scenario  400 F involves a handover from an S-DU to a T-DU. In this scenario, the base station  104 A includes a CU  172 , an S-DU  174 A, and a T-DU  174 B. Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  4 F  and  FIGS.  4 B- 4 E  are discussed below. 
     In the scenario  400 F, the UE  102  initially communicates  402 F data (e.g., UL data PDUs and/or DL data PDUs) with the base station  104  via the S-DU  174 A. The base station  104  performs a need for gap information procedure  450 F with the UE  102  via the S-DU  174 A to obtain a NeedForGapsInfo from the UE  102 . The need for gap information procedure  450 F is generally similar to the need for gap information procedure  350 A, with the S-DU  174 A in the procedure  450 F performing similar functions as the DU  174  in the procedure  350 A. 
     Next, the CU  172  initiates  407 F handover from the S-DU  174 A to the T-DU  174 B. The CU  172  and the T-DU  174 B perform a UE Context Setup procedure  460 F. The procedure  460 F is similar to the UE Context Setup procedure  460 B, with the T-DU  174 B performing similar functions as the T-DU  174  in the procedure  460 B. 
     After the UE Context Setup procedure  460 F, the CU  172  sends  472 F a handover command message including a MeasConfig including a MeasGapConfig to the S-DU  174 A. The handover command message also includes a T-DU configuration for the T-DU  174 B. The S-DU  174 A transmits  474 F the handover command message to the UE  102 , which performs  475 F a random access procedure with the T-DU  174 B. After the random access procedure successfully completes, the UE  102  sends  477 F a handover complete message to the T-DU  174 B, which sends  478 F the handover complete message to the CU  172 . The events  472 F,  474 F,  475 F,  477 F, and  478 F are collectively referred to in  FIG.  4 F  as a handover procedure  470 F. 
     After the handover procedure  470 F, the UE communicates  479 F with the base station  104 A via the T-DU  174 B in accordance with the MeasConfig and T-DU configuration in the handover command message. 
     In some implementations, as described with respect to  FIG.  4 B  and  FIG.  4 D , the CU  172  may include the MeasConfig including the MeasGapConfig in an RRC reconfiguration message and transmit  418 F the RRC reconfiguration message to the T-DU  174 B after the handover. The T-DU  174 B can transmit  420 F the RRC reconfiguration message to the UE  102 . In response, the UE  102  transmits  422 F an RRC reconfiguration complete message to the T-DU  174 B, which in turn transmits  424 F the RRC reconfiguration complete message to the CU  172 . The events  418 F,  420 F,  422 F, and  424 F are collectively referred to in  FIG.  3 F  as a measurement configuration procedure  480 F. 
     The UE  102  applies the MeasGapConfig to perform measurements on a frequency in accordance with the MeasGapConfig. The UE  102  transmits  426 F a measurement report message including the measurement results to the T-DU  174 B, which in turn transmits  426 F the measurement report message to the CU  172 . The events  426 F and  428 F are collectively referred to in  FIG.  3 F  as a measurement reporting procedure  490 F. 
     Now referring to  FIG.  4 G , a scenario  400 G involves a handover from an S-DU to a T-DU. In this scenario, the base station  104 A includes a CU  172 , an S-DU  174 A, and a T-DU  174 B. Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  4 G  and  FIGS.  4 B- 4 F  are discussed below. 
     In contrast to  FIG.  4 F , after the CU  172  initiates  407 G handover from the S-DU  174 A to the T-DU  174 B, the CU  172  and the T-DU  174 B perform a UE Context Setup procedure  460 G. The UE Context Setup procedure  460 G is similar to the UE Context Setup procedure  460 C, with the T-DU  174 B performing similar functions as the T-DU  174  in the procedure  460 C. 
     After the UE Context Setup procedure  460 G, the CU  172  sends  472 G a handover command message including a T-DU configuration to the S-DU  174 A. The handover command message does not include a MeasGapConfig because the T-DU  174 B does not generate a MeasGapConfig during the UE Context Setup procedure  460 G. The S-DU  174 A sends  474 G the handover command to the UE  102 , which performs  475 G a random access procedure with the T-DU  174 B. After the random access procedure successfully completes, the UE  102  sends  477 G a handover complete message to the T-DU  174 B, which sends  478 G the handover complete message to the CU  172 . The events  472 G,  474 G,  475 G,  477 G, and  478 G are collectively referred to in  FIG.  4 G  a handover procedure  470 G. 
     After the handover procedure  470 G, the UE communicates  479 G with the base station  104 A via the T-DU  174 B in accordance with the T-DU configuration in the handover command message. 
     In some implementations, the base station  104 A and the UE  102  may also perform a measurement configuration procedure  480 G. The measurement configuration procedure  480 G is similar to the measurement configuration procedure  480 F, except that any MeasConfig included in the RRC reconfiguration messages will not include a MeasGapConfig because the T-DU  174 B does not generate a MeasGapConfig during the UE Context Setup procedure  460 G. 
     Now referring to  FIG.  4 H , a scenario  400 H involves a handover from an S-DU to a T-DU. The scenario  400 H is generally similar to the scenario  400 F, and events similar to those discussed above are labeled with the same reference numbers. However, in contrast to  FIG.  4 F , in scenario  400 H, the CU  172  and the T-DU  174 B perform a UE Context Setup procedure  460 H rather than the UE Context Setup procedure  460 F. The UE Context Setup procedure  460 H is similar to the UE Context Setup procedure  460 D, with the T-DU  174 B performing similar functions as the T-DU in the procedure  460 D. 
     Now referring to  FIG.  4 I , a scenario  400 I involves a handover from an S-DU to a T-DU. The scenario  400 I is generally similar to the scenario  400 G, and events similar to those discussed above are labeled with the same reference numbers. However, in contrast to  FIG.  4 G , in scenario  400 I, the CU  172  and the T-DU  174 B perform a UE Context Setup procedure  460 I rather than the UE Context Setup procedure  460 G. The UE Context Setup procedure  460 I is similar to the UE Context Setup procedure  460 E, with the T-DU  174 B performing similar functions as the T-DU in the procedure  460 E. 
       FIGS.  5 A- 5 D  depict techniques for managing measurement gap configurations in scenarios in which the UE operates in dual connectivity (DC) with an MN and an SN. The scenarios depicted by  FIGS.  3 A- 3 D and  4 A- 4 I  can also correspond to DC scenarios, with the base station  104 A (and/or the base station  104 B, as in  FIGS.  4 A- 4 E ) operating as an MN. However, the  FIGS.  5 A- 5 D  are relevant to functionality than an SN can implement. Even if the UE  102  has already provided a NeedForGapsInfo IE to the MN  104 A, the UE  102  and the base stations  104 A,  106 A, and  106 B may still perform the techniques discussed below with reference to  FIGS.  5 A- 5 D . The measurement gap capability of the UE  102  may depend on whether the UE  102  is operating in SC or in DC. For example, when operating in DC, the UE  102  may need to use a receiver to communicate with an SN that the UE used to measure gaps while the UE  102  operated in SC. 
     Referring next to  FIG.  5 A , the base station  104 A in a scenario  500 A operates as an MN, and the base station  106 A operates as an SN. Initially, the UE  102  communicates  502 A data (e.g., UL Data PDUs and/or DL Data PDUs) with MN  104 A. In one case, the UE  102  in SC with the MN  104 A communicates  502 A data with the MN  104 A. In another case, the UE  102  communicates  502 A in DC with the MN  104 A and SN  106 B. In this case, the SN  106 B is a source SN (S-SN) and the SN  106 A is a target SN (T-SN). 
     Later in time, the MN  104 A can determine  532 A that it should initiate an SN Addition procedure to configure the base station  106 A as an SN for the UE  102 . In one implementation, the MN  104 A can make this determination based on one or more measurement results received from the UE  102 , for example, or another suitable event. In another implementation, the MN  104 A receives from the S-SN  106 B an SN Change Required message requesting an SN change to the T-SN  106 A, and makes this determination in response to the SN Change Required message. In response to the determination  532 A, the MN  104  sends  534 A an SN Addition Request message to the SN  106 A to initiate an SN Addition procedure. In response to receiving  534 A the SN Addition Request message, the SN  106 A includes an SN configuration in an SN Addition Request Acknowledge message for the UE  102 . The SN  106 A then sends  538 C the SN Addition Request Acknowledge message to the MN  104 , in response to the SN Addition Request message. 
     In some implementations, the MN  104 A can include a first NeedForGapsInfo in the SN Addition Request message if the MN  104 A stores the first NeedForGapsInfo. For example, the MN  104 A can receive the first NeedForGapsInfo from the UE  102  by performing a need for gap information procedure similar to the need for gap information procedure  450 A. In another example, the MN  104 A can receive the first NeedForGapsInfo from another base station (e.g., base station  104 B or S-SN  106 B) in an interface message, e.g., an Xn interface message, Handover Request message, SN Change Required message, or Retrieve UE Context Response message. In another example, the MN  104 A can receive the first NeedForGapsInfo from the CN  110  (e.g., MME  114  or AMF  164 ). In other implementations, the SN Addition Request message does not include a NeedForGapsInfo. 
     If the SN Addition Request message includes the first NeedForGapsInfo, the SN  106 A can determine to include or exclude a MeasGapConfig in the SN configuration according to the first NeedForGapsInfo, similar to the determination made by the CU  172  or the DU  174  in events  414 B,  413 C,  411 D, or  409 E. If the SN  106 A determines to include a MeasGapConfig in an RRC reconfiguration message according to the first NeedForGapsInfo, the SN  106 A can include a first MeasGapConfig in the SN configuration. Otherwise, the SN  106 A does not include a MeasGapConfig in the SN configuration. 
     The MN  104 A includes the SN configuration in an RRC container message and transmits  542 A the RRC container message to the UE  102 . In response to the RRC container message, the UE  102  transmits  543 A an RRC container response message to the MN  104 A. The UE  102  can include an RRC reconfiguration complete message in the RRC container response message. The MN  104 A transmits  544 A an SN Reconfiguration Complete message including the RRC reconfiguration complete message to the SN  106 A. In response to the SN configuration, the UE  102  performs  546 A a random access procedure with the SN  106 A via cell  126 A (i.e., PSCell) to connect to the SN  106 A, e.g., using one or more random access configurations in the SN configuration. After the UE  102  successfully completes the random access procedure (i.e., the SN  106 A identifies the UE  102  during the random access procedure), the UE  102  communicates  548 A control signals and data (e.g., UL data PDUs or DL data PDUs) with the SN  106 A via the PSCell  126 A using configurations in the SN configuration. The events  502 A,  532 A- 548 A are collectively referred to in  FIG.  5 A  as a DC configuration procedure  530 A. 
     After the SN  106 A connects to the UE  102 , the SN  106 A can send  504 A an RRC reconfiguration message including a second NeedForGapsConfig to the MN  104 A which in turn transmits  506 A the RRC reconfiguration message to the UE  102 . In response to the second NeedForGapsConfig, the UE  102  includes a second NeedForGapsInfo in an RRC reconfiguration complete message. The UE  102  transmits  508 A the RRC reconfiguration complete message to the MN  104 A in response to the RRC reconfiguration message. The MN  104 A in turn sends  510 A the RRC reconfiguration complete message to the SN  106 A. The events  504 A,  506 A,  508 A and  510 A are collectively referred to in  FIG.  5 A  as a need for gap information procedure  550 A. 
     In some implementations, the SN  106 A may indicate one or more frequency bands, for which the UE  102  is to indicate whether gaps are needed to perform measurements, in the second NeedForGapsConfig. In one implementation, the SN  106 A generates a requestTargetBandFilterNR field which includes one or more frequency band indicators (e.g., FreqBandIndicatorNR IEs) indicating the one or more frequency bands and includes the requestTargetBandFilterNR field in the second NeedForGapsConfig. In the second NeedForGapsInfo, the UE  102  indicates whether gaps are needed to perform measurements for the one or more frequency bands. In one implementation, in the second NeedForGapsInfo, the UE  102  does not indicate whether gaps are needed to perform measurements for one or more additional frequency bands not indicated by the SN  106 A in the second NeedForGapsConfig. With this implementation, the UE  102  saves power by not using bits to indicate whether gaps are needed to perform measurements for the one or more additional frequency bands. In another implementation, the UE  102  indicates, in the second NeedForGapsInfo, whether gaps are needed to perform measurements for one or more additional frequency bands not indicated by the SN  106 A in the second NeedForGapsConfig. With this implementation, the SN  106 A does not need to initiate another need for gap information procedure (similar to  550 A) to request the UE  102  to provide another NeedForGapsInfo indicating whether gaps are needed to perform measurements for one or more additional frequency bands. 
     In other implementations, the SN  106 A does not indicate a frequency band in the second NeedForGapsConfig. In one such implementation, if the SN  106 A does not indicate a frequency band in the second NeedForGapsConfig, the UE  102  can determine frequency band(s) for which the UE  102  will indicate measurement gap requirements in the second NeedForGapsInfo. The UE  102  can determine the frequency band(s) based on a PLMN identity of an operator operating the MN  104 A or the SN  106 A. For example, the UE  102  may store first band information associated with a first PLMN identity, which indicates first frequency band(s) owned by a first operator identified by the first PLMN identity. The UE  102  can generate the second NeedForGapsInfo which indicates whether gaps are needed to perform measurements for the first frequency band(s) in the first band information if the MN  104 A or the SN  106 A is operated by the first operator. The UE  102  may store second band information associated to a second PLMN identity, which indicates second frequency band(s) owned by a first operator identified by the first PLMN identity. The UE  102  can generate the second NeedForGapsInfo which indicates whether gaps are needed to perform measurements for the second frequency band(s) in the second band information if the MN  104 A or the SN  106 A is operated by the second operator. 
     Alternatively, the UE  102  can directly store a second NeedForGapsInfo indicating whether gaps are needed to perform measurements for frequency band(s) owned by a first operator identified by a first PLMN identity, and transmits  534 A the RRC reconfiguration complete message including the second NeedForGapsInfo if the base station  104 A or the SN  106 A is operated by the first operator. The UE  102  can directly store a third NeedForGapsInfo indicating whether gaps are needed to perform measurements for frequency band(s) owned by a second operator identified by a second PLMN identity, and transmits  534 A the RRC reconfiguration complete message including the second NeedForGapsInfo if the MN  104 A or the SN  106 A is operated by the second operator. Note, the stored second/third NeedForGapsInfo may or may not in the same format as the second/third NeedForGapsInfo transmitted in the RRC reconfiguration message. If the formats are different, the UE  102  converts the stored format to the transmitted format. 
     In another implementation, if the SN  106 A does not indicate a frequency band in the second NeedForGapsConfig, the UE  102  indicates whether gaps are needed to perform measurements in the second NeedForGapsInfo for all frequency band(s) the UE supports. 
     Thus, the SN  106 A can receive the first NeedForGapsInfo for the UE  102  from the MN  104 A in an SN Addition Request message (as in event  534 A), or can receive the second NeedForGapsInfo via the need for gap information procedure  550 A. In some implementations, the SN  106 A may receive both the first NeedForGapsInfo and the second NeedForGapsInfo. For example, the SN  106 A may request  504 A measurement gap capability information relating to different frequencies than the first NeedForGapsInfo. In other implementations, the SN  106 A receives either the first NeedForGapsInfo or the second NeedForGapsInfo. 
     After the SN  106 A connects to the UE 102  or after the need for gap information procedure  550 A (if performed), the SN  106 A can determine  514 A to include or exclude a MeasGapConfig in an RRC reconfiguration message based on the first NeedForGapsInfo (if received at event  534 A) or the second NeedForGapsInfo  510 A (if received at event  510 A), similar to the determination made by the CU  172  or the DU  174  in events  314 A,  313 B,  311 C, or  309 D. If the SN  106 A determines to include a MeasGapConfig in an RRC reconfiguration message based on the first/second NeedForGapsInfo, the SN  106 A can include a second MeasGapConfig in the RRC reconfiguration message. Otherwise, the SN  106 A does not include a MeasGapConfig in the RRC reconfiguration message. The SN  106 A sends  518 A the RRC reconfiguration message to the MN  104 A which in turn transmits  520 A the RRC reconfiguration message to the UE  102 . In response to the RRC reconfiguration message, the UE  102  transmits  522 A an RRC reconfiguration complete message to the MN  104 A which in turn sends  524 A the RRC reconfiguration complete message to the SN  106 A. The events  518 A,  520 A,  522 A and  524 A are collectively referred to in  FIG.  5 A  as a measurement configuration  580 A. 
     After the UE  102  receives the second MeasGapConfig, the UE  102  can measure one or more carrier frequencies during gaps configured by the second MeasGapConfig. The UE  102  may be configured by the SN  106 A to measure the one or more carrier frequencies before, during or after receiving the second MeasGapConfig. In some implementations, the SN  106 A can include the second MeasGapConfig in a first measurement configuration (MeasConfig) and include the first MeasConfig in the RRC reconfiguration message  518 A. In the first MeasConfig, the SN  106 A may configure the UE  102  to measure a first carrier frequency in a frequency band using gaps configured in the second MeasGapConfig. Alternatively, the SN  106 A may perform another measurement configuration procedure similar to event  380 A to transmit to the UE  102  a second MeasConfig. The second MeasConfig does not include a MeasGapConfig and configures the UE  102  to measure the first carrier frequency in a frequency band using gaps configured in the second MeasGapConfig. The SN  106 A may perform an additional measurement configuration procedure similar to event  580 A to transmit the UE  102  a third MeasConfig, which does not include a MeasGapConfig and configures the UE  102  to measure a second carrier frequency in a frequency band using gaps configured in the second MeasGapConfig. The first and second carrier frequencies can be in the same frequency band or different frequency bands. In other implementations, the SN  106 A may include the second MeasConfig in the SN configuration instead of a RRC reconfiguration message in a measurement configuration procedure. 
     In implementations in which the UE  102  receives (i) a first MeasConfig including a MeasGapConfig, and (ii) a second MeasConfig not including a MeasGapConfig, the second MeasConfig does not override the previously-received MeasGapConfig. The UE  102  can continue to use the MeasGapConfig received in the first MeasConfig to configure measurement gaps for target frequencies indicated in the second MeasConfig. 
     In some implementations, the SN  106 A can include a third NeedForGapsConfig, which indicates one or more additional frequency bands, in the RRC reconfiguration message  518 A. The UE  102  indicates whether gaps are needed to perform measurements for the one or more additional frequency bands in a fourth NeedForGapsInfo, and includes the fourth NeedForGapsInfo in the RRC reconfiguration complete message  522 A. the SN  106 A may determine to whether to generate a MeasGapConfig according to the fourth NeedForGapsInfo as described above. If the SN  106 A generates a third MeasGapConfig, the SN  106 A can transmit the third MeasGapConfig to the UE  102  in a similar way and the UE  102  can use the third MeasGapConfig, as described above. 
     In other implementations, the SN  106 A does not include a NeedForGapsConfig in the RRC reconfiguration message  518 A and the UE  102  does not include a NeedForGapsInfo in the RRC reconfiguration complete message  522 A. In such implementations, instead of including a third NeedForGapsConfig in the RRC reconfiguration message  518 A, the SN  106 A can include a third NeedForGapsConfig in an additional need for gap information procedure similar to the procedure  550 A. The SN  106 A can also repeat procedures similar to  514 A- 580 A after performing the additional need for gap information procedure. 
     The UE  102  applies the MeasGapConfig above to perform measurements on a carrier frequency which can be configured by the SN  106 A as described above. If the MeasGapConfig includes a GapConfig, the UE  102  performs measurements on gaps configured by the GapConfig, for example. In another example, if the MeasGapConfig indicates that the UE  102  should release a GapConfig, the UE  102  can perform measurements without using gaps. The UE  102  obtains a measurement result from the measurements, includes the measurement result in a measurement report message, and transmits  526 A a measurement report message to the MN  104 A. The MN  104 A in turn sends  528 A the measurement report message to the SN  106 A. For example, the measurement result can indicate a value of a reference signal received power (RSRP), reference signal received quality (RSRQ), Received Signal Strength Indicator (RSSI), or signal to noise and interference ratio (SINR). According to the measurement result, the SN  106 A can decide whether to configure or release an SCell for the UE  102  or change the PSCell  126 A to another cell (e.g., cell  124 B). For example, if the measurement result associated to a cell is above a predetermined threshold, the SN  106 A can configure the cell as an SCell for the UE  102 . In another example, if the measurement result associated with an SCell is above a predetermined threshold, the SN  106 A can release the SCell for the UE  102 . In yet another example, if the measurement result associated with a cell is above a predetermined threshold, the SN  106 A can configure the UE  102  to change the PSCell  126 A to the cell. The events  526 A and  528 A are collectively referred to in  FIG.  5 A  as a measurement reporting procedure  590 A. 
     In some implementations, the MN  104 A can receive a UE capability of the UE  102  from the UE  102 , the core network  110 , or another base station (e.g., base station  104 B) as described for  FIG.  3 A . The MN  104 A can include the UE capability in the SN Addition Request message. In some implementations, the MN  104 A can include UE capability in a CG-ConfigInfo IE and include the CG-ConfigInfo IE in the SN Addition Request message. 
     In some implementations, the UE  102  may indicate, in the UE capability, one or more frequency bands supported by the UE  102  for communicating with an SN. For example, the UE capability can include a supportedBandListNR field which includes one or more BandNR IEs indicating one or more frequency bands supported by the UE  102 . In another example, the UE capability can include a supportedBandCombinationList field (or BandCombinationList IE) which includes one or more FreqBandIndicatorNR IEs indicating one or more frequency bands supported by the UE  102 . In some implementations, the SN  106 A can determine (or select) the one or more frequency bands to include in the NeedForGapsConfig from the frequency bands supported by the UE  102 . In other implementations, the SN  106 A can include a frequency band in the NeedForGapsConfig that is not supported by the UE  102 . If the UE  102  does not support a frequency band indicated in the NeedForGapsConfig, the UE  102  in some implementations determines the NeedForGapsConfig is valid and ignores the frequency band. In this case, in one implementation, the UE  102  does not indicate whether gaps are needed for the unsupported frequency band in the NeedForGapsInfo. In another implementation, the UE  102  can indicate whether gaps are needed for the unsupported frequency band in the NeedForGapsInfo even though the indication is meaningless. 
     In other implementations, if the UE  102  does not support a frequency band indicated in the NeedForGapsConfig, the UE  102  determines the NeedForGapsConfig is invalid. In response to the determination, the UE  102  initiates an RRC connection reestablishment procedure. In the RRC connection reestablishment procedure, the UE  102  transmits an RRCReestablishmentRequest message to the MN  104 A or another base station (e.g., base station  104 B). The UE  102  receives a RRCReestablishment message from the MN  104 A or another base station (e.g., the base station  104 B) in response to the RRCReestablishmentRequest message. The UE  102  can transmit a RRCReestablishmentComplete message to the RRCReestablishment message. 
     The SN configuration can include one or more configuration parameters for the UE  102  to communicate with the SN  106 A. The SN configuration can include one or more random access configurations needed by the UE  102  to connect to the SN  106 A, and in some implementations, includes additional fields, such as a mobility field (e.g., mobilityControlInfo field or a reconfigurationWithSync field), which can include some or all of the random access configurations. The multiple configuration parameters can also configure zero, one or more SCells, configure PCell  124 B, and/or configure a physical layer configuration, a MAC configuration, and a RLC configuration. For example, the SN configuration can include a CellGroupConfig IE. In some implementations, the SN configuration can be an RRC reconfiguration message. 
     In some implementations, if the SN  106 A is a gNB, the RRC reconfiguration message and the RRC reconfiguration complete message can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. In other implementations, if the SN  106 A is an eNB or an ng-eNB, the RRC reconfiguration message and the RRC reconfiguration complete message can be an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. 
     In some implementations, if the MN  104 A is a gNB, the RRC container message and the RRC container response message can be an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively. In other implementations, if the MN  104 A is an eNB or an ng-eNB, the RRC container message and the RRC container response message can be an RRCConnectionReconfiguration message and an RRCConnectionReconfigurationComplete message, respectively. 
     Referring now to  FIG.  5 B , a scenario  500 B also involves a DC scenario in which the base station  104 A operates as an MN, and the base station  106 A operates as an SN. Events in this scenario similar to those discussed above are labeled with the same reference numbers. The differences between the scenarios of  FIG.  5 B  and  FIG.  5 A  are discussed below. 
     In  FIG.  5 B , the SN  106 A, MN  104 A, and the UE  102  may perform a DC configuration procedure  530 B, which is generally similar to the DC configuration procedure  530 A. As in  FIG.  5 A , the SN  106 A may receive a first NeedForGapsInfo from the MN  104 A during the DC Configuration procedure  530 B. 
     Next, in contrast to the need for gap information procedure  550 A, the SN  106 A may receive a second NeedForGapsInfo directly from the UE  102 . The SN  106 A transmits  503 B an RRC reconfiguration message including a second NeedForGapsConfig to the UE  102 . The event  503 B is generally similar to the event  504 A, except that the SN  106 A transmits  503 B the RRC reconfiguration message to the UE  102  rather than to the MN  104 A. In response, the UE  102  transmits  505 B an RRC reconfiguration complete message including a second NeedForGapsInfo to the SN  106 A. The events  503 B and  505 B are collectively referred to herein as a need for gap information procedure  550 B. 
     Similarly to  FIG.  5 B , the SN  106 A can receive both the first NeedForGapsInfo at event  530 B and the second NeedForGapsInfo at event  550 B, or can receive either the first NeedForGapsInfo or the second NeedForGapsInfo. Based on the first or the second NeedForGapsInfo, the SN  106 A can determine  514 B to include or exclude a MeasGapConfig in an RRC reconfiguration message, similar to the determinations made by the CU  172  or the DU  174  in events  314 A,  313 B,  311 C, or  309 D. 
     If the SN  106 A determines to include a MeasGapConfig based on the first or the second NeedForGapsInfo, the SN  106 A can include a second MeasGapConfig in an RRC reconfiguration message. Otherwise, the SN  106 A does not include a MeasGapConfig in the RRC reconfiguration message. The SN  106  sends  521 B the RRC reconfiguration message to the UE  102 , and the UE  102  transmits  523 B an RRC reconfiguration complete message to the SN  106 A in response. The UE  102  can perform measurements in accordance with the MeasGapConfig and transmit  529 B the measurement results to the SN  106 A in a measurement report. 
     Referring now to  FIG.  5 C , a scenario  500 C also involves a DC scenario in which the base station  104 A operates as an MN, and the base station  106 A operates as an SN. Events in this scenario similar to those discussed above are labeled with the same reference numbers. The scenario  500 C is generally similar to the scenario  500 A, but with the SN  106 A implementing the techniques as a distributed base station including a CU  172  and a DU  174 . 
     In particular, The CU  172  receives  534 C an SN Addition Request message, which may include a first NeedForGapsInfo, from the MN  104 A. The CU  172  transmits  536 C a UE Context Setup Request message to the DU  174 . In response, the DU  174  generates a DU configuration and transmits  537 C a UE Context Setup Response message including the DU configuration to the CU  172 . The CU  172  transmits  538 C an SN Addition Request Acknowledgement message containing an RRC reconfiguration and a CU configuration to the MN  104 A. The RRC reconfiguration includes the DU configuration. The MN  104  in turn transmits  542 C an RRC container message including the DU configuration and the CU configuration to the UE  102 . In response, the UE  102  transmits  543 C an RRC container response message to the MN  104 A, and the MN  104  transmits  544 C an SN Reconfiguration Complete message to the CU  172 . 
     The UE  102  then performs  546 C a random access procedure with the SN  106 A via the DU  174 . After the UE  102  successfully completes the random access procedure, the UE  102  communicates  548 C control signals and data (e.g., UL data PDUs or DL data PDUs) with the SN  106 A. The events  502 C,  532 C- 548 C are collectively referred to in  FIG.  5 C  as a DC configuration procedure  530 C. 
     After the SN  106 A connects to the UE  102 , the SN  106 A may receive a second NeedForGapsInfo in a need for gap information procedure  550 C. The need for gap information procedure  550 C can be similar to the need for gap information procedures  350 A,  550 A, or  550 B, for example. In some implementations, the SN  106 A receives both the first NeedForGapsInfo and the second NeedForGapsInfo. In other implementations, the SN  106 A receives the first NeedForGapsInfo or the second NeedForGapsInfo. 
     Based on the first NeedForGapsInfo (received by the SN  106 A at event  534 C), or the second NeedForGapsInfo (received by the SN  106 A at event  550 C), the SN  106 A determines in a UE Context Modification procedure  560 C whether to generate or not generate a MeasGapConfig for the UE  102 . The CU  172  and the DU  174  of the SN  106 A can make this determination using the techniques discussed with reference to events  360 A,  360 B,  360 C, or  360 D. The SN  106 A transmits a MeasConfig, which may or may not include a MeasGapConfig, to the UE  102  via a measurement configuration procedure  580 C, which may be similar to the measurement configuration procedures  380 A or  380 B. Based on the MeasConfig, the UE  102  can perform measurements and transmit a measurement report including the measurement results to the SN  106 A in a measurement reporting procedure  590 C, which may be similar to the measurement reporting procedure  390 A. 
     Referring now to  FIG.  5 D , a scenario  500 D also involves a DC scenario in which the base station  104 A operates as an MN, and the base station  106 A operates as an SN. Events in this scenario similar to those discussed above are labeled with the same reference numbers. The scenario  500 D is generally similar to the scenario  500 C, but with the SN  106 A performing a UE context setup procedure during a DC configuration procedure rather than after a DC configuration procedure. 
     More particularly, after the CU  172  receives  534 D an SN Addition Request including a first NeedForGapsInfo, the CU  172  and the DU  174  of the SN  106 A perform a UE Context Setup procedure  560 D. The UE Context Setup procedure  560 D may be similar to the UE Context Setup procedures  460 B,  460 C,  460 D, and  460 E. Events  538 D- 548 D may then proceed in a similar manner as events  538 C to  548 C. The events  502 D,  532 D- 548 D are collectively referred to herein as a DC configuration procedure  530 D. 
     After the DC configuration procedure  530 D, the SN  106 A transmits a MeasConfig, which may or may not include a MeasGapConfig, to the UE  102  via a measurement configuration procedure  580 D or in the RRC reconfiguration message  538 D, which may be similar to the measurement configuration procedures  380 A or  380 B. Based on the MeasConfig, the UE  102  can perform measurements and transmit a measurement report including the measurement results to the SN  106 A in a measurement reporting procedure  590 D, which may be similar to the measurement reporting procedure  390 A. 
       FIGS.  6 A,  6 B . and  7  depict RRC resume scenarios in which a DU and a CU can implement the techniques discussed above for managing measurement gap capability information. 
     Now referring to  FIG.  6 A , a scenario  600 A involves an RRC resume scenario in which the base station  104 A operates as a T-BS of an RRC resume procedure and includes a T-DU  174  and a T-CU  172 . The base station  106 A operates as a S-BS of the RRC resume procedure. Initially, the UE  102  operates in an RRC connected stale and communicates  602 A with the S-BS  104 B in accordance with an S-BS configuration. The S-BS  104 B determines  652 A to suspend the RRC connection between the S-BS  104 B and the UE  102 . Accordingly, the S-BS  104 B transmits  653 A an RRC release message to the UE  102 . In response, the UE  102  transitions  654 A to a state with a suspended RRC connection (e.g., an RRC_INACTIVE state or an RRC_IDLE state). 
     To resume an RRC connection with the RAN  105 , the UE  102  transmits  655 A an RRC resume request message to the T-BS  104 B by transmitting the RRC resume request message to the T-DU  174 . The T-DU sends  656 A the RRC resume request message to the T-CU  172 . The T-CU  172  then transmits  657 A a Retrieve UE Context Request message to the S-BS  104 B. In response, the S-BS  104 B transmits  658 A a Retrieve UE Context Response message including an S-BS configuration to the T-CU  172 . 
     Next, the T-CU  172  sends  659 A a UE Context Setup Request message to the T-DU  174 , which in turn transmits  660 A a UE Context Setup Response message including a T-DU configuration to the T-CU  172 . The T-CU  172  sends  661 A an RRC resume message including the T-DU configuration and a NeedForGapsConfig to the T-DU  174 , which in turn sends  662 A the RRC resume message to the UE  102 . 
     In response to the RRC resume message, the UE  102  transitions  663 A to a connected state (e.g., RRC_CONNECTED) and transmits  664 A an RRC resume complete message including a NeedForGapsInfo to the T-DU  174 . The UE  102  generates the NeedForGapsInfo in accordance with the NeedForGapsConfig, as discussed above with reference to  FIG.  3 A . 
     The T-DU  174  transmits  665 A the RRC resume complete message including the NeedForGapsInfo to the T-CU  172 . The T-BS  104 A then performs a UE Context Modification procedure  660 A, which may be similar to any one of UE Context Modification procedures  360 A,  360 B,  360 C, or  360 D. The T-BS  104 A perform the measurement configuration procedure  380 A, which may be similar to measurement configuration procedure  380 A or  380 B. The UE  102  can transmit a measurement report to the T-BS  104 A in a measurement reporting procedure  690 A. which may be similar to the measurement reporting procedure  390 A. 
     Now referring to  FIG.  6 B , a scenario  500 B also involves an RRC resume scenario in which the base station  104 A operates as a T-BS of an RRC resume procedure and includes a T-DU  174  and a T-CU  172 . The base station  104 B operates as a S-BS of an RRC resume procedure.  FIG.  6 B  is generally similar to  FIG.  6 A , but with the S-BS  104 B rather than the UE  102  providing a NeedForGapsInfo to the T-BS  104 A. 
     The scenario  600 B begins in a similar manner as the scenario  600 A. However, after receiving  657 B the Retrieve UE Context Request message, the S-BS  104 B transmits  658 B a Retrieve UE Context Response message including both an S-BS configuration and a NeedForGapsInfo to the T-CU  172 . The S-BS  104 B may store a NeedForGapsInfo received previously, for example, during an earlier need for gap information procedure such as the need for gap information procedure  450 A. 
     The T-CU  172  and the T-DU  174  of the T-BS  104 A can determine, based on the NeedForGapsInfo, whether to generate a MeasGapConfig during a UE Context Setup procedure  660 B, which may be similar to any one of the UE Context Setup procedures  460 B,  460 C,  460 D, or  460 E. Following the UE Context Setup procedure  660 B, the T-CU  172  transmits  661 B an RRC resume message including a T-DU configuration to the T-DU  174 , which in turn transmits  662 B the RRC resume message to the UE  102 . The T-CU  172  may or may not include a MeasGaptConfig in the RRC resume message, depending on whether the T-DU  174  generated a MeasGapConfig during the UE Context Setup procedure  660 B. In some implementations, even if the T-DU  174  generated a MeasGapConfig during the UE Context Setup procedure  660 B, the T-CU  172  determines not to include die MeasGapConfig in the RRC resume message. Instead, the T-CU  172  may send a later RRC message, such as an RRC reconfiguration message, including the MeasGapConfig to the UE  102  via the T-DU  174 . If the T-BS  104 B does not generate a MeasGapConfig, the T-BS  104 B may still transmit (at event  662 B or in a later RRC message) a MeasConfig that does not include a MeasGapConfig to the UE  102 . 
     In response to the RRC resume message, the UE  102  transitions  663 B to a connected state (e.g., RRC_CONNECTED) and transmits  664 B an RRC resume complete message to the T-DU  174 , which in turn transmits  665 B the RRC resume complete message to the T-CU  172 . 
     After resuming the RRC connection with the T-BS  104 B and after receiving a MeasConfig, which may or may not include a MeasGapConfig, from the T-BS  104 B (either at event  662 B or by receiving another RRC message), the UE  102  performs measurements in accordance with the MeasConfig. The UE  102  includes the measurement results in a measurement report message and transmits  626 B the measurement report message to the T-DU  174 , which in turn transmits  628 B the measurement report message to the T-CU  172 . 
       FIG.  7    depicts a scenario  700  involving an RRC resume scenario when a UE is operating in dual connectivity with an MN and an SN. The base station  104 A operates as an S-MN and the base station  106 A operates as an S-SN of the RRC resume scenario. The base station  104 B operates as a T-MN and the base station  106 B operates as a T-SN of the RRC resume scenario. The T-MN  104 B includes both a T-DU  174  and a T-CU  172 . 
     Initially, the UE  102  operates in an RRC connected state and (1) communicates  702  in SC with the S-MN  104 A using an S-MN configuration, or (2) communicates  702  in DC with the S-MN  104 A using an S-MN configuration and with the S-SN  106 A using an S-SN configuration. The S-MN  104 A determines  752  to suspend the RRC connection between the S-MN  104 A and the UE  102 . Accordingly, the S-MN  104 A transmits  753  an RRC release message to the UE  102 . In response, the UE  102  transitions  754  to a state with a suspended RRC connection (e.g., an RRC_INACTIVE state or an RRC_IDLE state). 
     To resume an RRC connection with the RAN  105 , the UE  102  transmits  755  an RRC resume request message to the T-DU  174 . The T-DU sends  756  the RRC resume request message to the T-CU  172 , which then transmits  757  a Retrieve UE Context Request message to the S-MN  104 A. In response, the S-MN  104 A transmits  758  a Retrieve UE Context Response message including an S-MN configuration to the T-CU  172 . 
     The UE Context Response message also includes a first NeedForGapsInfo (i.e., NeedForGapsInfo1) and a second NeedForGapsInfo (i.e., NeedForGapsInfo2). The NeedForGapsInfo1 is to be used by the T-MN  104 B for configuring measurement gaps for the UE  102 , and the NeedForGapsInfo2 is to be used by the T-SN  106 B for configuring measurement gaps for the UE  102 . 
     Based on the NeedForGapsInfo1, the T-CU  172  and the T-DU  174  of the T-MN perform a UE Context Setup procedure  760 , which can be similar to any one of UE Context Setup procedures  460 B,  460 C,  460 D, or  460 E. The T-CU  172  then transmits  761  an RRC resume message to the T-DU  174 . The RRC resume message includes a T-DU configuration, and may also include a MeasGapConfig, depending on whether the T-DU  174  generated a measurement gap configuration during the UE Context Setup procedure  760 . After the UE  102  receives the MeasGapConfig, the UE  102  can measure one or more carrier frequencies during gaps configured by the MeasGapConfig. The UE  102  may be configured by the CU  172  to measure the one or more carrier frequencies during or after receiving the MeasGapConfig. For example, the CU  172  includes a first MeasConfig configuring the UE  102  to measure a carrier frequency in the RRC resume message. The CU  172  can include the MeasGapConfig in the first MeasConfig. 
     The T-DU  174  transmits  762  the RRC resume message to the UE  102 . In response, the UE  102  transitions  763  to a connected state (e.g., RRC_CONNECTED) and transmits  764  an RRC resume complete message to the T-DU  174 . The T-DU  174  transmits  765  the RRC resume complete message to the T-CU  172 . 
     In some implementations, even if the T-DU generated a MeasGapConfig during the UE Context Setup procedure  760 , the T-CU  172  determines not to include the MeasGapConfig in the RRC resume message. Instead, the T-CU  172  may send a later RRC message, such as an RRC reconfiguration message, including the MeasGapConfig to the UE  102  via the T-DU  174 . If the T-MN  104 B does not generate a MeasGapConfig, the T-MN  104 B may still transmit (at event  762  or in a later RRC message) a second MeasConfig that does not include a MeasGapConfig to the UE  102 . The second MeasConfig can configure the UE  102  to measure carrier frequencies. 
     After resuming the RRC connection with the T-MN  104 B and after receiving a MeasConfig, which may or may not include a MeasGapConfig, from the T-MN  104 B (either at event  762  or by receiving another RRC message), the UE  102  performs measurements in accordance with the MeasConfig. The UE  102  includes the measurement results in a measurement report message and transmits  726  the measurement report message to the T-DU  174 , which in turn transmits  728  the measurement report to the T-CU  172 . 
     In addition, the UE  102 , the T-MN  104 B, and the T-SN  106 B can perform  779  (i) the DC configuration procedure  530 D using the NeedForGapsInfo2, or (ii) the DC configuration procedure  530 C using the NeedForGapsInfo2 and the UE Context Modification procedure  560 C, in order to provide the NeedForGapsInfo2 to the T-SN  106 B. For example, the T-MN  104 B can provide the NeedForGapsInfo2 in an SN Addition Request to the T-SN  106 B, as in events  534 C and  534 D. In one implementation, the T-SN  106 B can perform the UE Context Setup procedure  560 D, included within the DC Configuration procedure  530 D. In another implementation, the T-SN  106 B can complete the DC Configuration procedure  530 D, and later perform the UE Context Setup procedure  560 C. 
     The T-SN  106 B can then perform a measurement configuration procedure  780 , which is similar to the measurement configuration procedure  580 A,  580 B if the T-SN  106 B generated a MeasGapConfig at event  779 , or to the measurement configuration procedure  380 B if the T-SN  106 B did not generate a MeasGapConfig at event  779 . The UE  102  reports the results of measurements that the UE performs in accordance with a MeasConfig, which may or may not include a MeasGapConfig, to the T-SN  106 B via a measurement reporting procedure  790 , which is similar to the measurement reporting procedure  590 A or  529 B. 
     For further clarity, several example methods which the devices operating in the systems of  FIGS.  1 A- 1 C  can implement are discussed next with reference to  FIGS.  8 - 16   . 
       FIG.  8    is a flow diagram depicting an example method  800 , implemented in a CU (e.g., the CU  172 ), for managing measurement gap capability information. At block  802 , the CU receives a NeedForGapsInfo IE (e.g., event  310 A during procedure  350 A or any one of events  350 B-D,  471 B-E,  450 F-I,  534 C,  550 C,  534 D,  665 A,  658 B, or  758 ). At block  804 , the CU sends a UE Context Request message including the NeedForGapsInfo IE to a DU (e.g., the DU  174 ) (e.g., any one of events  312 A-D during the procedures  360 A-D, respectively;  412 B-E during the procedures  460 B-E, respectively:  460 F-I,  560 C-D,  660 A-B,  760 ,  779 ). Depending on the implementation and/or scenario, the UE Context Request can be a UE Context Modification Request or a UE Context Setup Request. 
     At block  806 , the CU receives a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) from the DU (e.g., any one of events  316 A-D during the procedures  360 A-D, respectively;  416 B-E during the procedures  460 B-E, respectively;  460 F-I,  560 C-D,  660 A-B,  760 ,  779 ). Depending on whether the DU generated a measurement gap configuration based on the NeedForGapsInfo, the UE Context Response message may or may not include a measurement gap configuration. 
       FIG.  9 A  is a flow diagram depicting an example method  900 A, implemented in a DU (e.g., the DU  174 ) for determining whether to generate a measurement gap configuration. At block  902 A, the DU receives a UE Context Request message (e.g., a UE Context Modification Request or a UE Context Setup Request) including a NeedForGapsInfo IE from a CU (e.g., the CU  172 ) (e.g., any one of events  312 A-D during the procedures  360 A-D, respectively;  412 B-E during the procedures  460 B-E, respectively;  460 F-I,  560 C-D,  660 A-B,  760 ,  779 ). 
     Next, at block  904 A, the DU determines whether the NeedForGapsInfo indicates that the UE requires gaps to measure a carrier frequency included in a MeasurementTimingConfiguration IE. If the NeedFor GapsInfo indicates that the UE requires measurement gaps, the flow proceeds to block  906 A. Otherwise, the flow proceeds to block  910 A. 
     At block  906 A, the DU generates a measurement gap configuration that the UE is to use to perform measurements on the carrier frequency (e.g., any one of events  314 A of procedure  360 A,  315 C of procedure  360 C,  414 B of procedure  460 B,  415 D of procedure  460 D). At block  908 A, the DU sends a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) including the measurement gap configuration to the CU (e.g., any one of events  316 A,  316 C,  416 B,  416 D). 
     Alternatively, if the flow proceeds to block  910 A, the DU does not generate a measurement gap configuration (e.g., event  313 B of procedure  350 B, procedure  360 D, event  413 C of procedure  460 C, procedure  460 E). If the DU receives SMTC information together with the NeedForGapsInfo, the DU can ignore the SMTC information. At block  912 A, the DU sends a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) not including a measurement gap configuration to the CU (e.g., any one of events  316 B,  316 D,  416 C,  416 E). 
       FIG.  9 B  is a flow diagram depicting an example method  900 B, implemented in a DU (e.g., the DU  174 ) for determining whether to generate a measurement gap configuration. At block  902 B, the DU receives a UE Context Request message (e.g., a UE Context Modification Request or a UE Context Setup Request) including a UE Capability (e.g., a NeedForGapsInfo IE, an interFrequencyMeas-NoGap field, a UE-NR-Capability IE, a UE-EUTRA-Capability IE, and/or a UE-MRDC-Capability IE) from a CU (e.g., the CU  172 ) (e.g., any one of events  312 A-F during the procedures  360 A-F, respectively;  412 B-E during the procedures  460 B-E, respectively;  460 F-I,  560 C-D,  660 A-B,  760 ,  779 ). 
     Next, at block  904 B, the DU determines whether the UE Capability indicates that the UE requires gaps to measure a carrier frequency. If the UE Capability indicates that the UE requires measurement gaps, the flow proceeds to block  906 B. Otherwise, the flow proceeds to block  910 B. 
     At block  906 B, the DU generates a measurement gap configuration that the UE is to use to perform measurements on the carrier frequency (e.g., any one of events  314 A of procedure  360 A,  315 C of procedure  360 C,  414 B of procedure  460 B,  415 D of procedure  460 D,  314 E of procedure  360 E). At block  908 B, the DU sends a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) including the measurement gap configuration to the CU (e.g., any one of events  316 A,  316 C,  416 B,  416 D,  316 E). 
     Alternatively, if the flow proceeds to block  910 B, the DU generates a measurement gap configuration which releases a gap configuration (e.g., any one of events  314 A of procedure  360 A,  315 C of procedure  360 C,  414 B of procedure  460 B,  415 D of procedure  460 D,  314 E of procedure  360 E). If the DU receives frequency information indicating the carrier frequency, and/or SMTC information together with the UE Capability, the DU can ignore the frequency information and/or SMTC information. At block  912 B, the DU sends a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) including the measurement gap configuration to the CU (e.g., any one of events  316 A,  316 C,  416 B,  416 D,  316 E). In alternatives to the blocks  910 B and  912 B, the DU does not generate a gap configuration configuring gaps for the UE and sends a UE Context Response message (e.g., a UE Context Modification Response or a UE Context Setup Response) excluding a measurement gap configuration to the CU. 
       FIG.  10    is a flow diagram depicting an example method  1000 , implemented in a CU (e.g., the CU  172 ) for determining whether to request gaps for a UE (e.g., the UE  102 ) in a message to a DU (e.g., the DU  174 ). At block  1002 , the CU receives a UE Capability (e.g., a NeedForGapsInfo IE, an interFrequencyMeas-NoGap field, a UE-NR-Capability IE, a UE-EUTRA-Capability IE, and/or a UE-MRDC-Capability IE) of the UE (e.g., event  310 A during procedure  350 A or any one of events  350 B-D,  471 B-E,  450 F-I,  534 C,  550 C,  534 D,  665 A,  658 B, or  758 ). 
     At block  1004 , the CU determines whether the UE Capability indicates that a UE requires measurement gaps to perform a measurement on a carrier frequency. If the UE does require measurement gaps, then the flow proceeds to block  1006 . Otherwise, the flow proceeds to block  1008 . At block  1006 , the CU determines to include information requesting that a DU configure gaps for the measured carrier frequency in a UE Context Request message and sends the UE Context Request message to the DU (e.g., events  311 C and  312 C, events  411 D and  412 D or events  1709 D and  1712 D). Alternatively, at block  1008 , the CU determines to exclude information requesting that a DU configure gaps for the measured carrier frequency from a UE Context Request message or include information (e.g., an indication or MeasConfig) requesting that a DU release gaps previously configured for the UE in a UE Context Request message and sends the UE Context Request message to the DU (e.g., events  309 D and  312 D, events  409 E and  412 E or events  1709 D and  1712 D). 
       FIG.  11    is a flow diagram depicting an example method  1100 , implemented in an S-BS (e.g., the S-BS  104 A), for managing measurement gap capability information during handover scenarios. The method begins at block  1102 , where the S-BS receives a NeedForGapsInfo IE from a UE (e.g., the UE  102 ), in an RRC Response message (e.g., event  408 A during procedure  450 A, or any one of events  450 B-E). 
     At block  1104 , the S-BS initiates handover to a network node for the UE. The network node can be, for example, a T-BS (e.g., the T-BS  104 B) (e.g., event  407 A), or a T-CU (e.g., the CU  172 ) (e.g., any one of events  407 B-E). At block  1106 , the S-BS sends a Handover Request message including the NeedForGapsInfo to the network node to enable the network node to determine whether to configure a measurement gap configuration (e.g., any one of events  471 A-E). 
     In some implementations, the method  1100  can be implemented by a CU (e.g., the CU  172 ). At  1102 , the CU receives a NeedForGapsInfo IE from a UE (e.g., the UE  102 ), via an S-DU (e.g., the S-DU  174 A) (e.g., any one of events  450 E- 450 I). At block  1104 , the CU initiates handover from the S-DU to a T-DU (e.g., the T-DU  174 B) (e.g., any one of events  407 F-I). With the T-DU, the CU performs a UE Context Setup procedure (e.g., any one of events  460 F-I). At block  1106 , the CU sends a handover command to the S-DU, which may or may not include a measurement gap configuration, depending on the outcome of the UE Context Setup procedure (e.g.,  472 F during procedure  470 F, event  472  during procedure  470 G, or any one of events  470 H-I). 
       FIG.  12    is a flow diagram depicting an example method  1200 , implemented in an S-BS (e.g., the S-BS  104 B), for managing measurement gap capability information following suspending an RRC connection. The method  1200  begins at block  1202 , where the S-BS receives a NeedForGapsInfo IE on an RRC connection in an RRC Response message from a UE (e.g., the UE  102 ) (e.g., any one of events  602 A-B,  702 ). 
     At block  1204 , the S-BS transmits an RRC Release message configuring the UE to suspend the RRC connection (e.g., any one of events  653 A-B,  753 ). At block  1206 , the S-BS receives a Retrieve UE Context Request message from a second base station (e.g., any one of events  657 A-B,  757 ). At block  1208 , the S-BS sends a Retrieve UE Context Response message including the NeedForGapsInfo to the second base station to enable to second base station to determine whether to configure a measurement gap configuration (e.g., any one of events  658 A-B,  758 ). 
       FIG.  13    is a flow diagram depicting an example method  1300 , implemented in a UE (e.g., the UE  102 ) for generating measurement gap capability information. At block  1302 , the UE  102  receives a NeedForGapsConfig IE (e.g., event  306 A during the procedure  350 A, procedures  350 B-D, event  406 A during the procedure  450 A, procedures  450 B-I, event  506 A during the procedure  550 A, event  503 B during the procedure  550 B, procedure  550 C, or event  662 A). At block  1304 , the UE determines whether the NeedForGapsConfig indicates one or more frequency band(s) that the UE does not support. If so, the flow proceeds to block  1306 . Otherwise, the flow proceeds immediately to block  1308 . 
     At block  1306 , the UE ignores the unsupported frequency band(s). Next, at block  1308 , the UE generates a NeedForGapsInfo IE for bands indicated in the NeedForGapsConfig that the UE does support. 
       FIG.  14    is a flow diagram depicting an example method  1400 , implemented in a base station (e.g., the base stations  104 A-B or  106 A-B) for requesting measurement gap capability information from a UE (e.g., the UE  102 ). At block  1402 , the base station receives, from the UE, an indication of frequency bands that the UE supports (e.g., any one of events  302 A-D,  402 A-I,  502 A,  502 C-D,  602 A-B,  702 ). At block  1404 , the base station generates a NeedForGapsConfig indicating one or more frequency band(s) that the UE supports, and the base station transmits an RRC message including the NeedForGapsConfig to the UE (e.g., event  306 A during the procedure  350 A, procedures  350 B-D, event  406 A during the procedure  450 A, procedures  450 B-I, event  506 A during the procedure  550 A, event  503 B during the procedure  550 B, procedure  550 C, or event  662 A). At block  1406 , the base station receives an RRC response message including a NeedForGapsInfo IE from the UE (e.g., event  308 A during the procedure  350 A, procedures  350 B-D, event  408 A during the procedure  450 A, procedures  450 B-I, event  508 A during the procedure  550 A, event  505 B during the procedure  550 B, procedure  550 C, or event  664 A). 
       FIG.  15    is a flow diagram of an example method  1500  for managing measurement gap information, which can be implemented in a first network node (e.g., a DU  174  or a base station) of a RAN (e.g., the RAN  105 ). At block  1502 , the first network node receives, from a second network node of the RAN, an indication of a measurement gap capability (e.g., a NeedForGapsInfoNR IE, an interFrequencyMeas-NoGap-r16 IE, first information requesting that the first network node configure measurement gaps for the UE or indicating that the first network node should not generate measurement gaps or should release previously configured measurement gaps, or a UE Context Request including or excluding measurement timing information, such as SMTC information) of the UE in communication with the RAN (e.g.,  312 A-F,  471 A,  412 B-E,  510 A). 
     At block  1504 , the first network node determines, based on the indication of the measurement gap capability, whether to generate a measurement gap configuration (e.g., a MeasGapConfig) for the UE (e.g., any one of events  314 A,  313 B,  315 C,  360 D,  414 A,  414 B,  413 C,  415 D, procedure  460 E,  514 A). 
     At block  1506 , the first network node provides, to the second network node, an indication of whether the first network node generated the measurement gap configuration for the UE (e.g., a message including or excluding a MeasGapConfig) (e.g., any one of events  316 A-D,  472 A,  416 B-E,  518 A). The first network node may generate and provide a first configuration to the second node, where the first configuration is a configuration that enables the UE to perform inter-frequency measurement on reference signal(s) (RS(s)) within an active DL BWP without measurement gaps (e.g., events  342 E or  342 F). 
     In an aspect similar to the example method  1500 , a first network node can receive an indication of a measurement gap capability of a UE from the UE. For example, when the first network node operates as an SN to provide DC to the UE, the SN can receive an indication of a measurement gap capability (e.g., a NeedForGapsInfoNR IE) from a second network node (e.g., from an MN, as in procedure  530 B) and/or directly from the UE (e.g., event  505 B). The SN can determine, based on the indication of the measurement gap capability, whether to generate a measurement gap configuration for the UE (e.g., event  514 B). The SN can provide an indication of whether the SN generated the measurement gap configuration by transmitting a message (e.g., a message including or excluding a MeasGapConfig) directly to the UE (e.g., event  521 B). 
       FIG.  16    is a flow diagram of another example method  1600  for managing measurement gap information, which can be implemented in a first network node (e.g., a CU  172  or a base station). At block  1602 , the first network node receives information element specifying a measurement gap capability (e.g., a NeedForGapsInfoNR IE, or an interFrequencyMeas-NoGap-r16 IE) of a user equipment (UE) in communication with the RAN (e.g., events  302 E or  302 F, or any one of events  310 A during the procedure  350 A,  350 B-D,  408 A,  471 B-D,  502 A,  502 C,  665 A,  658 B,  758 ). 
     At block  1604 , the first network node transmits, to a second network node, an indication of the measurement gap capability (e.g., a NeedForGapsInfoNR IE, an interFrequencyMeas-NoGap-r16 IE, first information requesting that the second network node configure measurement gaps for the UE or indicating that the second network node should not generate measurement gaps or should release previously configured measurement gaps, or a UE Context Request including or excluding measurement timing information, such as SMTC information) (e.g., any one of events  312 A-F,  471 A,  412 B-E,  534 A,  510 A,  534 C,  534 D). At block  1606 , receives, from the second network node, an indication of whether the second network node generated a measurement gap configuration for the UE (e.g., a message including or excluding a MeasGapConfig) (e.g., any one of events  316 A-D,  472 A,  416 B-E,  518 A,  538 D). Alternatively or in addition, the first network node may receive a first configuration from the second network node, or generate a first configuration if the first network node does not receive the first configuration, where the first configuration is a configuration that enables the UE to perform inter-frequency measurement on reference signal(s) (RS(s)) within an active DL BWP without measurement gaps (e.g., events  342 E or  342 F). 
       FIG.  17    is a flow diagram of an example method  1700  for managing gap measurement, which can be implemented in a UE (e.g., the UE  102 ) of this disclosure. At block  1702 , the UE receives a configuration the UE is to use to report a measurement gap capability (e.g., a NeedForGapsConfig) (e.g., any one of events  306 A of procedure  350 A,  406 A of procedure  450 A,  506 A of procedure  550 A,  503 B of procedure  550 B,  662 A). 
     Next, at block  1704 , the UE determines that the configuration specifies at least one frequency band that is unsupported at the UE (e.g., block  1302  of  FIG.  13   ). At block  1706 , the UE generates an indication of a measurement gap capability (e.g., a NeedForGapsInfoNR IE) based on the received configuration (e.g., block  1308  of  FIG.  13   ). 
     At block  1708 , the UE transmits the indication of the measurement gap capability to the RAN (e.g., any one of events  308 A of procedure  350 A,  408 A of procedure  450 A,  508 A of procedure  550 A,  505 B of procedure  550 B,  664 A). 
     The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure: 
     Example 1. A method in a first network node of a radio access network (RAN) for managing measurement gap information, the method comprising: receiving, at the first network node from a second network node of the RAN, an indication of a measurement gap capability of a UE in communication with the RAN; determining, by processing hardware and based on the indication of the measurement gap capability, whether to generate a measurement gap configuration for the UE; and providing, to the second network node, an indication of whether the first network node generated the measurement gap configuration for the UE. 
     Example 2. The method of example 1, further comprising: generating, by the processing hardware and in response to the determining, the measurement gap configuration for the UE. 
     Example 3. The method of example 2, wherein the providing includes: transmitting a message including the measurement gap configuration to the second network node. 
     Example 4. The method of example 2, wherein the generating includes: generating the measurement gap configuration indicating one or more measurement gaps the UE is to use to perform measurements on a frequency. 
     Example 5. The method of example 2, wherein the generating includes: generating the measurement gap configuration indicating that the UE is to release a previous measurement gap configuration. 
     Example 6. The method of any one of examples 2-5, wherein the receiving includes: receiving measurement timing information. 
     Example 7. The method of any one of examples 2-5, wherein the receiving includes: receiving a request to generate the measurement gap configuration. 
     Example 8. The method of example 1, wherein the providing includes: in response to determining to not generate the measurement gap configuration, transmitting a measurement configuration that does not include the measurement gap configuration. 
     Example 9. The method of example 8, wherein the receiving includes: receiving a request to modify or to set up a context of the UE, the request not including measurement timing information or an information element specifying the measurement gap capability. 
     Example 10. The method of example 8, wherein the receiving includes: receiving a request to modify or to set up a context of the UE, the request not including an information element requesting the first node to generate the measurement gap configuration. 
     Example 11. The method of example 8, wherein the receiving includes: receiving a dedicated information element indicating that the first node should not generate the measurement gap configuration. 
     Example 12. The method of any one of examples 1-5 or 7-11, wherein the receiving includes: receiving an information element specifying the measurement gap capability. 
     Example 13. The method of example 12, wherein the information element indicates whether the UE can perform inter-frequency synchronization signal block (SSB) measurements without measurement gaps. 
     Example 14. The method of example 13, wherein: the method further comprises, based on the information element, generating a configuration the UE is to use to perform inter-frequency measurements on reference signals within an active BWP of the UE without measurement gaps; and providing the configuration to the second network node. 
     Example 15. The method of any one of examples 1-14, wherein the receiving includes: receiving the indication in a request to modify or to set up a context of the UE. 
     Example 16. The method of any one of example 1-8 or 12-14, wherein the receiving includes: receiving the indication in a request to perform a handover. 
     Example 17. The method of any one of examples 1-8 or 12-14, wherein the receiving includes: receiving the indication in a request that the first network node operate as a secondary node (SN) to provide dual connectivity (DC) to the UE. 
     Example 18. The method of any one of examples 1-17, wherein the providing includes: transmitting a response to a request to modify a context of the UE. 
     Example 19. The method of any one of examples 1-17, wherein the providing includes: transmitting a response to a request to set up a context of the UE. 
     Example 20. The method of any one of examples 1-17, wherein the providing includes: transmitting a handover command 
     Example 21. The method of any one of examples 1-17, wherein the providing includes: transmitting a command to reconfigure a radio connection, the command associated with a protocol for controlling radio resources. 
     Example 22. The method of any one of examples 1-21, wherein the providing includes: providing the indication from a distributed unit (DU) of a distributed base station to a central unit (CU) of the distributed base station. 
     Example 23. The method of any one of examples 1-21, wherein the providing includes: providing the indication from a first base station to a second base station. 
     Example 24. A method in a first network node of a radio access network (RAN) for managing measurement gap information, the method comprising: receiving an information element specifying a measurement gap capability of a user equipment (UE) in communication with the RAN; transmitting, to a second network node of the RAN, an indication of the measurement gap capability; and receiving, from the second network node, an indication of whether the second network node generated a measurement gap configuration for the UE. 
     Example 25. The method of example 24, wherein receiving the indication includes: receiving the measurement gap configuration. 
     Example 26. The method of example 24, wherein receiving the indication includes: receiving a message that does not include the measurement gap configuration. 
     Example 27. The method of any one of examples 24-26, wherein the transmitting the indication includes: determining, based on the information element, whether the UE requires measurement gaps to perform measurements on a target frequency band; and if the UE requires measurement gaps, transmitting measurement timing information to the second network node. 
     Example 28. The method of any one of examples 24-26, wherein: the information element is a first information element; and transmitting the indication includes: determining, based on the first information element, whether the UE requires measurement gaps to perform measurements on a target frequency band; and if the UE requires measurement gaps, transmitting a second information element requesting the second node to generate the measurement gap configuration. 
     Example 29. The method of any of examples 24-26, wherein: the information element is a first information element; and transmitting the indication includes: determining, based on the first information element, whether the UE requires measurement gaps to perform measurements on a target frequency band; and if the UE does not require measurement gaps, transmitting a second information element requesting the second node to not generate the measurement gap configuration or to release a previously configured measurement gap configuration. 
     Example 30. The method of any one of examples 24-29, wherein transmitting the indication includes: transmitting the information element. 
     Example 31. The method of any one of examples 24-30, wherein receiving the information element includes: receiving a message indicating completion of a radio connection reconfiguration, the message including the information element and conforming to a protocol for controlling radio resources. 
     Example 32. The method of any one of examples 24-30, wherein receiving the information element includes: receiving a message indicating completion of a procedure for resuming a radio connection, the message including the information element and conforming to a protocol for controlling radio resources. 
     Example 33. The method of any one of examples 24-30, wherein receiving the information element includes: receiving a request to perform a handover, the request including the information element. 
     Example 34. The method of any one of examples 24-30, wherein receiving the information element includes: receiving a request to initiate a secondary node (SN) addition procedure, the request including the information element. 
     Example 35. The method of any one of examples 24-30, wherein receiving the information element includes: receiving a response to a request to retrieve a context of the UE, the response including the information element. 
     Example 36. The method of any one of examples 24-35, wherein receiving the information element includes: receiving the information element at a central unit (CU) of a distributed base station from a distributed unit (DU) of the distributed base station. 
     Example 37. The method of any one of examples 24-35, wherein receiving the information element includes: receiving the information element from the UE. 
     Example 38. The method of any one of examples 24-35, wherein receiving the information element includes: receiving the information element at a first base station from a second base station. 
     Example 39. The method of example 38, wherein receiving the information element includes: receiving the information element at a central unit (CU) of the first base station from the second base station. 
     Example 40. The method of any one of examples 24-39, wherein transmitting the indication includes: transmitting a request to modify a context of the UE, the request including the indication. 
     Example 41. The method of any one of examples 24-39, wherein transmitting the indication includes: transmitting a request to set up a context of the UE, the request including the indication. 
     Example 42. The method of any one of examples 24-39, wherein transmitting the indication includes: transmitting a request to perform a handover, the request including the indication. 
     Example 43. The method of any one of examples 24-39, wherein transmitting the indication includes: transmitting a message indicating completion of a procedure for resuming a radio connection, the message including the indication and the message conforming to a protocol for controlling radio resources. 
     Example 44. The method of any one of examples 24-33 or 35-39, wherein transmitting the indication includes: transmitting a request that the second network node operate as secondary node (SN) to provide dual connectivity (DC) to the UE, the request including the indication. 
     Example 45. The method of any one of examples 24-44, wherein transmitting the indication includes: transmitting the indication from a central unit (CU) of a distributed base station to a distributed unit (DU) of the distributed base station. 
     Example 46. The method of any one of examples 24-44, wherein transmitting the indication includes: transmitting the indication from a first base station to a second base station. 
     Example 47. The method of any one of examples 24-46, further comprising: receiving a measurement report from the UE while the UE is operating in single connectivity (SC) with the RAN. 
     Example 48. The method of any one of examples 24-46, further comprising: not receiving a measurement report from while the UE is operating in dual connectivity (DC) with the RAN, wherein the UE suspends performing measurements while operating in DC. 
     Example 49. The method of any of examples 24-48, wherein information element indicates whether the UE can perform inter-frequency synchronization signal block (SSB) measurements without measurement gaps. 
     Example 50. The method of example 49, wherein: transmitting the indication of the measurement gap capability includes transmitting the information element; and receiving the indication of whether the second network node generated the measurement gap configuration includes receiving a configuration the UE is to use to perform inter-frequency measurements on reference signals within the active BWP of the UE without measurement gaps. 
     Example 51. The method of example 49, further comprising: generating, based on the information element, a configuration the UE is to use to perform inter-frequency measurements on reference signals within the active BWP of the UE without measurement gaps. 
     Example 52. A network node of a radio access network (RAN) comprising processing hardware and configured to implement a method of any of examples 1-51. 
     Example 53. A method in a user equipment (UE) for managing gap measurement, the method comprising: receiving, by processing hardware and from a radio access network (RAN), a configuration the UE is to use to report a measurement gap capability; determining, by the processing hardware, that the configuration specifies at least one frequency band unsupported at the UE; generating, by the processing hardware, an indication of a measurement gap capability based on the received configuration; and transmitting, by the processing hardware, the indication of the measurement gap capability to the RAN. 
     Example 54. The method of example 53, wherein generating the indication includes omitting the at least one frequency band unsupported at the UE from the indication. 
     Example 55. The method of example 53, wherein generating the indication includes specifying the at least one frequency band unsupported at the UE in the indication. 
     Example 56. The method of any of examples 53-55, wherein the configuration is a NeedForGapsConfig information element (IE). 
     Example 57. The method of any of examples 53-56, wherein the indication is a NeedForGapsInfo IE. 
     Example 58. The method of any of examples 53-57, further comprising: receiving, by the processing hardware from the RAN, a measurement gap configuration; and performing, by the processing hardware, one or more measurements in accordance with the measurement gap configuration. 
     Example 59. The method of example 58, wherein the measurement gap configuration is a NeedForGapsConfig information element (IE). 
     Example 60. The method of any of examples 53-59, further comprising: determining that the measurement gap configuration is valid. 
     Example 61. The method of any of examples 53-60, wherein the receiving includes: receiving a message including the configuration from a central unit (CU) of a distributed base station, via a distributed unit (DU) of the distributed base station. 
     Example 62. The method of example 61, wherein the message is a command to reconfigure a radio connection, the command associated with a protocol for controlling radio resources. 
     Example 63. A user equipment (UE) comprising processing hardware and configured to implement a method of any of examples 53-62. 
     The following description may be applied to the description above. 
     A user device in which the techniques of this disclosure can be implemented (e.g., the UE  102 ) 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 comprise 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), etc.) to perform certain operations. A hardware module may also comprise 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. 
     When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.