PATENT DOCUMENT

Publication Number: US-11991571-B2
Application Number: US-201917276017-A
Country: US
Kind Code: B2

Title: Conditional handover in wireless networks

Abstract:
An apparatus of a user equipment (UE) includes processing circuitry, where to configure the UE for conditional handover between a source base station (SBS) and a target base station (TBS) in a wireless network, the processing circuitry is to decode measurement configuration information from the SBS. The measurement configuration information indicating a measurement event and a first threshold associated with the measurement event to trigger measurement reporting. A measurement report is encoded for transmission to the SBS, the measurement report triggered based on the first threshold. RRC signaling is received from the SBS. The RRC signaling includes a conditional handover command indicating a second threshold for the measurement event, the second threshold being higher than the first threshold. A handover from the SBS to the TBS is performed based on the conditional handover command after detecting that the measurement event satisfies the second threshold.

Claims:
What is claimed is: 
     
       1. A method, comprising:
 at a user equipment device (UE), in association with a conditional handover between a source base station (SBS) and a target base station (TBS) in a wireless network:
 receiving, from the SBS, measurement configuration information, the measurement configuration information indicating a first threshold associated with a measurement event related to the TBS, wherein the first threshold is for triggering measurement reporting; 
 comparing a measurement associated with the measurement event to the first threshold; 
 in response to the comparison, transmitting, to the SBS, a measurement report; and 
 receiving, from the SBS, radio resource control (RRC) signaling, the RRC signaling including a conditional handover command for handover from the SBS to the TBS, the conditional handover command associated with a second threshold for the measurement event, wherein the conditional handover command is based on a handover acknowledgement from the TBS responsive to a conditional handover request form the SBS to the TBS, wherein the RRC signaling further includes an offset for exiting the conditional handover. 
 
 
     
     
       2. The method of  claim 1 , wherein the conditional handover command originates from the TBS. 
     
     
       3. The method of  claim 1 , wherein the conditional handover command includes a random access channel (RACH) resource. 
     
     
       4. The method of  claim 3 , further comprising:
 performing a RACH procedure with the TBS during the handover, using the RACH resource. 
 
     
     
       5. The method of  claim 3 , wherein the RRC signaling further includes a timer to indicate how long the RACH resource is valid. 
     
     
       6. The method of  claim 1 ,
 wherein, in response to a non-conditional handover command, an RRC connection is terminated between the UE and the SBS, and 
 wherein, in response to the conditional handover command, an RRC connection between the UE and the SBS is not terminated until after the second threshold is satisfied by the measurement event. 
 
     
     
       7. A method, comprising:
 at a source base station (SBS), in order to configure the SBS for conditional handover between the SBS and a target base station (TBS) in a wireless network:
 encoding measurement configuration information for transmission to a user equipment (UE), the measurement configuration information indicating a first threshold associated with a measurement event related to the TBS, wherein the first threshold is for triggering measurement reporting; 
 decoding a measurement report from the UE, the measurement report triggered based on the first threshold associated with the measurement event; 
 encoding a handover request for transmission to the TBS including a conditional handover request; 
 decoding a handover acknowledgement from the TBS, the handover acknowledgement received in response to the handover request and including a conditional handover command for transmission to the UE; and 
 encoding radio resource control (RRC) signaling for transmission to the UE, the RRC signaling including the conditional handover command for handover from the SBS to the TBS, the conditional handover command associated with a second threshold for the measurement event, wherein the RRC signaling further includes an offset for exiting the conditional handover. 
 
 
     
     
       8. The method of  claim 7 , further comprising:
 encoding a handover request for transmission to the TBS. 
 
     
     
       9. The method of  claim 8 , further comprising:
 decoding a handover acknowledgement from the TBS, the handover acknowledgement received in response to the handover request and including the conditional handover command for transmission to the UE. 
 
     
     
       10. The method of  claim 9 , wherein the handover acknowledgement further includes:
 a random access channel (RACH) resource for use by the UE for a RACH procedure, and 
 an indication of how long the RACH resource will be available. 
 
     
     
       11. The method of  claim 8 , further comprising:
 decoding a handover completion message from the TBS, wherein the handover completion message indicates completion of the conditional handover; and 
 encoding a resource release message for transmission to at least a second target base station for releasing of resources reserved for handover with the UE. 
 
     
     
       12. The method of  claim 7 , wherein the measurement report from the UE includes measurements triggered based on the first threshold and associated with the target base station and at least a second target base station, further comprising:
 encoding a second handover request for transmission to the second target base station, wherein the handover acknowledgement is further received in response to the second handover request and including a second conditional handover command from the second target base station for transmission to the UE. 
 
     
     
       13. The method of  claim 7 , wherein the handover acknowledgement further includes
 the second threshold for the measurement event. 
 
     
     
       14. A method, comprising:
 at a target base station (TBS), in association with a conditional handover of a user equipment (UE) between a source base station (SBS) and the TBS in a wireless network:
 receiving, from the SBS, an early handover request; and 
 transmitting, to the SBS, a handover acknowledgement, the handover acknowledgement comprising:
 a conditional handover command for handover from the SBS to the TBS; and 
 a timer for a period of contention-free random access channel (RACH) procedure (CFRA), wherein a contention-based RACH procedure (CBRA) is to be used for the conditional handover after expiration of the timer. 
 
 
 
     
     
       15. The method of  claim 14 , wherein the conditional handover command originates from the TBS. 
     
     
       16. The method of  claim 14 , wherein the conditional handover command includes a random access channel (RACH) resource. 
     
     
       17. The method of  claim 16 , further comprising:
 performing a RACH procedure with the UE during the handover, using the RACH resource. 
 
     
     
       18. The method of  claim 14 , further comprising:
 transmitting, to the SBS, a handover completion message, wherein the handover completion message indicates completion of the conditional handover. 
 
     
     
       19. The method of  claim 14 , further comprising:
 determining to accept the early handover request. 
 
     
     
       20. The method of  claim 14 , wherein the handover acknowledgement further includes a threshold for a measurement event.

Description:
PRIORITY CLAIM 
     This application is a U.S. National Stage filing of International Application No. PCT/US2019/050622, filed Sep. 11, 2019, titled “Conditional Handover in Wireless Networks”, which claims the benefit of priority to the U.S. Provisional Application No. 62/733,820, filed Sep. 20, 2018, titled “CONDITIONAL HANDOVER”. All of the aforementioned applications are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     Aspects pertain to wireless communications. Some aspects relate to wireless networks including 3GPP (Third Generation Partnership Project) networks, 3GPP LTE (Long Term Evolution) networks, 3GPP LTE-A (LTE Advanced) networks, and fifth-generation (5G) networks including 5G new radio (NR) (or 5G-NR) networks and 5G-LTE networks. Other aspects are directed to systems and methods for conditional handover in wireless networks. 
     BACKGROUND 
     Mobile communications have evolved significantly from early voice systems to today&#39;s highly sophisticated integrated communication platform. With the increase in different types of devices communicating with various network devices, usage of 3GPP LTE systems has increased. The penetration of mobile devices (user equipment or UEs) in modern society has continued to drive demand for a wide variety of networked devices in a number of disparate environments. Fifth-generation (5G) wireless systems are forthcoming and are expected to enable even greater speed, connectivity, and usability. Next generation 5G networks (or NR networks) are expected to increase throughput, coverage, and robustness and reduce latency and operational and capital expenditures. 5G-NR networks will continue to evolve based on 3GPP LTE-Advanced with additional potential new radio access technologies (RATs) to enrich people&#39;s lives with seamless wireless connectivity solutions delivering fast, rich content and services. As current cellular network frequency is saturated, higher frequencies, such as millimeter wave (mmWave) frequency, can be beneficial due to their high bandwidth. 
     Potential LTE operation in the unlicensed spectrum includes (and is not limited to) the LTE operation in the unlicensed spectrum via dual connectivity (DC), or DC-based LAA, and the standalone LTE system in the unlicensed spectrum, according to which LTE-based technology solely operates in unlicensed spectrum without requiring an “anchor” in the licensed spectrum, called MulteFire. MulteFire combines the performance benefits of LTE technology with the simplicity of Wi-Fi-like deployments. 
     Further enhanced operation of LTE systems in the licensed as well as unlicensed spectrum is expected in future releases and 5G systems. Such enhanced operations can include techniques for conditional handover in wireless networks. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       In the figures, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The figures illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. 
         FIG.  1 A  illustrates an architecture of a network, in accordance with some aspects. 
         FIG.  1 B  and  FIG.  1 C  illustrate a non-roaming 5G system architecture in accordance with some aspects. 
         FIG.  2    illustrates a swimlane diagram of a conditional handover, in accordance with some aspects. 
         FIG.  3    illustrates a swimlane diagram of a conditional handover with more than one target cells, in accordance with some aspects. 
         FIG.  4    illustrates events for conditional handover and legacy handover, in accordance with some aspects. 
         FIG.  5    illustrates a block diagram of a communication device such as an evolved Node-B (eNB), a new generation Node-B (gNB), an access point (AP), a wireless station (STA), a mobile station (MS), or a user equipment (UE), in accordance with some aspects. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and the drawings sufficiently illustrate aspects to enable those skilled in the art to practice them. Other aspects may incorporate structural, logical, electrical, process, and other changes. Portions and features of some aspects may be included in or substituted for, those of other aspects. Aspects set forth in the claims encompass all available equivalents of those claims. 
       FIG.  1 A  illustrates an architecture of a network in accordance with some aspects. The network  140 A is shown to include user equipment (UE)  101  and UE  102 . The UEs  101  and  102  are illustrated as smartphones (e.g., handheld touchscreen mobile computing devices connectable to one or more cellular networks) but may also include any mobile or non-mobile computing device, such as Personal Data Assistants (PDAs), pagers, laptop computers, desktop computers, wireless handsets, drones, or any other computing device including a wired and/or wireless communications interface. The UEs  101  and  102  can be collectively referred to herein as UE  101 , and UE  101  can be used to perform one or more of the techniques disclosed herein. 
     Any of the radio links described herein (e.g., as used in the network  140 A or any other illustrated network) may operate according to any exemplary radio communication technology and/or standard. 
     LTE and LTE-Advanced are standards for wireless communications of high-speed data for UE such as mobile telephones. In LTE-Advanced and various wireless systems, carrier aggregation is a technology according to which multiple carrier signals operating on different frequencies may be used to carry communications for a single UE, thus increasing the bandwidth available to a single device. In some aspects, carrier aggregation may be used where one or more component carriers operate on unlicensed frequencies. 
     Aspects described herein can be used in the context of any spectrum management scheme including, for example, dedicated licensed spectrum, unlicensed spectrum, (licensed) shared spectrum (such as Licensed Shared Access (LSA) in 2.3-2.4 GHz, 3.4-3.6 GHz, 3.6-3.8 GHz, and further frequencies and Spectrum Access System (SAS) in 3.55-3.7 GHz and further frequencies). 
     Aspects described herein can also be applied to different Single Carrier or OFDM flavors (CP-OFDM, SC-FDMA, SC-OFDM, filter bank-based multicarrier (FBMC), OFDMA, etc.) and in particular 3GPP NR (New Radio) by allocating the OFDM carrier data bit vectors to the corresponding symbol resources. 
     In some aspects, any of the UEs  101  and  102  can comprise an Internet-of-Things (IoT) UE or a Cellular IoT (CIoT) UE, which can comprise a network access layer designed for low-power IoT applications utilizing short-lived UE connections. In some aspects, any of the UEs  101  and  102  can include a narrowband (NB) IoT UE (e.g., such as an enhanced NB-IoT (eNB-IoT) UE and Further Enhanced (FeNB-IoT) UE). An IoT UE can utilize technologies such as machine-to-machine (M2M) or machine-type communications (MTC) for exchanging data with an MTC server or device via a public land mobile network (PLMN), Proximity-Based Service (ProSe) or device-to-device (D2D) communication, sensor networks, or IoT networks. The M2M or MTC exchange of data may be a machine-initiated exchange of data. An IoT network includes interconnecting IoT UEs, which may include uniquely identifiable embedded computing devices (within the Internet infrastructure), with short-lived connections. The IoT UEs may execute background applications (e.g., keep-alive messages, status updates, etc.) to facilitate the connections of the IoT network. 
     In some aspects, any of the UEs  101  and  102  can include enhanced MTC (eMTC) UEs or further enhanced MTC (FeMTC) UEs. 
     The UEs  101  and  102  may be configured to connect, e.g., communicatively couple, with a radio access network (RAN)  110 . The RAN  110  may be, for example, an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), a NextGen RAN (NG RAN), or some other type of RAN. The UEs  101  and  102  utilize connections  103  and  104 , respectively, each of which comprises a physical communications interface or layer (discussed in further detail below); in this example, the connections  103  and  104  are illustrated as an air interface to enable communicative coupling, and can be consistent with cellular communications protocols, such as a Global System for Mobile Communications (GSM) protocol, a code-division multiple access (CDMA) network protocol, a Push-to-Talk (PTT) protocol, a PTT over Cellular (POC) protocol, a Universal Mobile Telecommunications System (UMTS) protocol, a 3GPP Long Term Evolution (LTE) protocol, a fifth-generation (5G) protocol, a New Radio (NR) protocol, and the like. 
     In an aspect, the UEs  101  and  102  may further directly exchange communication data via a ProSe interface  105 . The ProSe interface  105  may alternatively be referred to as a sidelink interface comprising one or more logical channels, including but not limited to a Physical Sidelink Control Channel (PSCCH), a Physical Sidelink Shared Channel (PSSCH), a Physical Sidelink Discovery Channel (PSDCH), and a Physical Sidelink Broadcast Channel (PSBCH). 
     The UE  102  is shown to be configured to access an access point (AP)  106  via connection  107 . The connection  107  can comprise a local wireless connection, such as, for example, a connection consistent with any IEEE 802.11 protocol, according to which the AP  106  can comprise a wireless fidelity (WiFi®) router. In this example, the AP  106  is shown to be connected to the Internet without connecting to the core network of the wireless system (described in further detail below). 
     The RAN  110  can include one or more access nodes that enable the connections  103  and  104 . These access nodes (ANs) can be referred to as base stations (BSs), NodeBs, evolved NodeBs (eNBs), Next Generation NodeBs (gNBs), RAN nodes, and the like, and can comprise ground stations (e.g., terrestrial access points) or satellite stations providing coverage within a geographic area (e.g., a cell). In some aspects, the communication nodes  111  and  112  can be transmission/reception points (TRPs). In instances when the communication nodes  111  and  112  are NodeBs (e.g., eNBs or gNBs), one or more TRPs can function within the communication cell of the NodeBs. The RAN  110  may include one or more RAN nodes for providing macrocells, e.g., macro RAN node  111 , and one or more RAN nodes for providing femtocells or picocells (e.g., cells having smaller coverage areas, smaller user capacity, or higher bandwidth compared to macrocells), e.g., low power (LP) RAN node  112 . 
     Any of the RAN nodes  111  and  112  can terminate the air interface protocol and can be the first point of contact for the UEs  101  and  102 . In some aspects, any of the RAN nodes  111  and  112  can fulfill various logical functions for the RAN  110  including, but not limited to, radio network controller (RNC) functions such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management. In an example, any of the nodes  111  and/or  112  can be a new generation Node-B (gNB), an evolved node-B (eNB), or another type of RAN node. 
     The RAN  110  is shown to be communicatively coupled to a core network (CN)  120  via an S1 interface  113 . In aspects, the CN  120  may be an evolved packet core (EPC) network, a NextGen Packet Core (NPC) network, or some other type of CN (e.g., as illustrated in reference to  FIGS.  1 B- 1     i ). In this aspect, the S1 interface  113  is split into two parts: the S1-U interface  114 , which carries traffic data between the RAN nodes  111  and  112  and the serving gateway (S-GW)  122 , and the S1-mobility management entity (MME) interface  115 , which is a signaling interface between the RAN nodes  111  and  112  and MMEs  121 . 
     In this aspect, the CN  120  comprises the MMEs  121 , the S-GW  122 , the Packet Data Network (PDN) Gateway (P-GW)  123 , and a home subscriber server (HSS)  124 . The MMEs  121  may be similar in function to the control plane of legacy Serving General Packet Radio Service (GPRS) Support Nodes (SGSN). The MMEs  121  may manage mobility aspects in access such as gateway selection and tracking area list management. The HSS  124  may comprise a database for network users, including subscription-related information to support the network entities&#39; handling of communication sessions. The CN  120  may comprise one or several HSSs  124 , depending on the number of mobile subscribers, on the capacity of the equipment, on the organization of the network, etc. For example, the HSS  124  can provide support for routing/roaming, authentication, authorization, naming/addressing resolution, location dependencies, etc. 
     The S-GW  122  may terminate the S1 interface  113  towards the RAN  110 , and routes data packets between the RAN  110  and the CN  120 . In addition, the S-GW  122  may be a local mobility anchor point for inter-RAN node handovers and also may provide an anchor for inter-3GPP mobility. Other responsibilities of the S-GW  122  may include a lawful intercept, charging, and some policy enforcement. 
     The P-GW  123  may terminate an SGi interface toward a PDN. The P-GW  123  may route data packets between the EPC network  120  and external networks such as a network including the application server  184  (alternatively referred to as application function (AF)) via an Internet Protocol (IP) interface  125 . The P-GW  123  can also communicate data to other external networks  131 A, which can include the Internet, IP multimedia subsystem (IPS) network, and other networks. Generally, the application server  184  may be an element offering applications that use IP bearer resources with the core network (e.g., UMTS Packet Services (PS) domain, LTE PS data services, etc.). In this aspect, the P-GW  123  is shown to be communicatively coupled to an application server  184  via an IP interface  125 . The application server  184  can also be configured to support one or more communication services (e.g., Voice-over-Internet Protocol (VoIP) sessions, PTT sessions, group communication sessions, social networking services, etc.) for the UEs  101  and  102  via the CN  120 . 
     The P-GW  123  may further be a node for policy enforcement and charging data collection. Policy and Charging Rules Function (PCRF)  126  is the policy and charging control element of the CN  120 . In a non-roaming scenario, in some aspects, there may be a single PCRF in the Home Public Land Mobile Network (HPLMN) associated with a UE&#39;s Internet Protocol Connectivity Access Network (IP-CAN) session. In a roaming scenario with a local breakout of traffic, there may be two PCRFs associated with a UE&#39;s IP-CAN session: a Home PCRF (H-PCRF) within an HPLMN and a Visited PCRF (V-PCRF) within a Visited Public Land Mobile Network (VPLMN). The PCRF  126  may be communicatively coupled to the application server  184  via the P-GW  123 . 
     In some aspects, the communication network  140 A can be an IoT network. One of the current enablers of IoT is the narrowband-IoT (NB-IoT). 
     An NG system architecture can include the RAN  110  and a 5G network core (5GC)  120 . The NG-RAN  110  can include a plurality of nodes, such as gNBs and NG-eNBs. The core network  120  (e.g., a 5G core network or 5GC) can include an access and mobility function (AMF) and/or a user plane function (UPF). The AMF and the UPF can be communicatively coupled to the gNBs and the NG-eNBs via NG interfaces. More specifically, in some aspects, the gNBs and the NG-eNBs can be connected to the AMF by NG-C interfaces, and to the UPF by NG-U interfaces. The gNBs and the NG-eNBs can be coupled to each other via Xn interfaces. 
     In some aspects, the NG system architecture can use reference points between various nodes as provided by 3GPP Technical Specification (TS) 23.501 (e.g., V15.4.0, 2018-12). In some aspects, each of the gNBs and the NG-eNBs can be implemented as a base station, a mobile edge server, a small cell, a home eNB, and so forth. In some aspects, a gNB can be a master node (MN) and NG-eNB can be a secondary node (SN) in a 5G architecture. 
       FIG.  1 B  illustrates a non-roaming 5G system architecture in accordance with some aspects. Referring to  FIG.  1 B , there is illustrated a 5G system architecture  140 B in a reference point representation. More specifically, UE  102  can be in communication with RAN  110  as well as one or more other 5G core (5GC) network entities. The 5G system architecture  140 B includes a plurality of network functions (NFs), such as access and mobility management function (AMF)  132 , session management function (SMF)  136 , policy control function (PCF)  148 , application function (AF)  150 , user plane function (UPF)  134 , network slice selection function (NSSF)  142 , authentication server function (AUSF)  144 , and unified data management (UDM)/home subscriber server (HSS)  146 . The UPF  134  can provide a connection to a data network (DN)  152 , which can include, for example, operator services, Internet access, or third-party services. The AMF  132  can be used to manage access control and mobility and can also include network slice selection functionality. The SMF  136  can be configured to set up and manage various sessions according to network policy. The UPF  134  can be deployed in one or more configurations according to the desired service type. The PCF  148  can be configured to provide a policy framework using network slicing, mobility management, and roaming (similar to PCRF in a 4G communication system). The UDM can be configured to store subscriber profiles and data (similar to an HSS in a 4G communication system). 
     In some aspects, the 5G system architecture  140 B includes an IP multimedia subsystem (IMS)  168 B as well as a plurality of IP multimedia core network subsystem entities, such as call session control functions (CSCFs). More specifically, the IMS  168 B includes a CSCF, which can act as a proxy CSCF (P-CSCF)  162 BE, a serving CSCF (S-CSCF)  164 B, an emergency CSCF (E-CSCF) (not illustrated in  FIG.  1 B ), or interrogating CSCF (I-CSCF)  166 B. The P-CSCF  162 B can be configured to be the first contact point for the UE  102  within the IM subsystem (IMS)  168 B. The S-CSCF  164 B can be configured to handle the session states in the network, and the E-CSCF can be configured to handle certain aspects of emergency sessions such as routing an emergency request to the correct emergency center or PSAP. The I-CSCF  166 B can be configured to function as the contact point within an operator&#39;s network for all IMS connections destined to a subscriber of that network operator, or a roaming subscriber currently located within that network operator&#39;s service area. In some aspects, the I-CSCF  166 B can be connected to another IP multimedia network  170 E, e.g. an IMS operated by a different network operator. 
     In some aspects, the UDM/HSS  146  can be coupled to an application server  160 E, which can include a telephony application server (TAS) or another application server (AS). The AS  160 B can be coupled to the IMS  168 B via the S-CSCF  164 B or the I-CSCF  166 B. 
     A reference point representation shows that interaction can exist between corresponding NF services. For example,  FIG.  1 B  illustrates the following reference points: N 1  (between the UE  102  and the AMF  132 ), N 2  (between the RAN  110  and the AMF  132 ), N 3  (between the RAN  110  and the UPF  134 ), N 4  (between the SMF  136  and the UPF  134 ), N 5  (between the PCF  148  and the AF  150 , not shown), N 6  (between the UPF  134  and the DN  152 ), N 7  (between the SMF  136  and the PCF  148 , not shown), N 8  (between the UDM  146  and the AMF  132 , not shown), N 9  (between two UPFs  134 , not shown), N 10  (between the UDM  146  and the SMF  136 , not shown), N 11  (between the AMF  132  and the SMF  136 , not shown), N 12  (between the AUSF  144  and the AMF  132 , not shown), N 13  (between the AUSF  144  and the UDM  146 , not shown), N 14  (between two AMFs  132 , not shown), N 15  (between the PCF  148  and the AMF  132  in case of a non-roaming scenario, or between the PCF  148  and a visited network and AMF  132  in case of a roaming scenario, not shown), N 16  (between two SMFs, not shown), and N 22  (between AMF  132  and NSSF  142 , not shown). Other reference point representations not shown in  FIG.  1 E  can also be used. 
       FIG.  1 C  illustrates a 5G system architecture  140 C and a service-based representation. In addition to the network entities illustrated in  FIG.  1 B , system architecture  140 C can also include a network exposure function (NEF)  154  and a network repository function (NRF)  156 . In some aspects, 5G system architectures can be service-based and interaction between network functions can be represented by corresponding point-to-point reference points Ni or as service-based interfaces. 
     In some aspects, as illustrated in  FIG.  1 C , service-based representations can be used to represent network functions within the control plane that enable other authorized network functions to access their services. In this regard, 5G system architecture  140 C can include the following service-based interfaces: Namf  158 H (a service-based interface exhibited by the AMF  132 ), Nsmf  1581  (a service-based interface exhibited by the SMF  136 ), Nnef  158 B (a service-based interface exhibited by the NEF  154 ), Npcf  158 D (a service-based interface exhibited by the PCF  148 ), a Nudm  158 E (a service-based interface exhibited by the UDM  146 ), Naf  158 F (a service-based interface exhibited by the AF  150 ), Nnrf  158 C (a service-based interface exhibited by the NRF  156 ), Nnssf  158 A (a service-based interface exhibited by the NSSF  142 ), Nausf  158 G (a service-based interface exhibited by the AUSF  144 ). Other service-based interfaces (e.g., Nudr, N5g-eir, and Nudsf) not shown in  FIG.  1 C  can also be used. 
     Techniques disclosed herein can be used to reduce user data interruption during handover (HO), which targets as close as possible to 0 ms (i.e., relaxed requirements could be considered) and improve robustness during handover. 
       FIG.  2    illustrates a swimlane diagram  200  of a conditional handover, in accordance with some aspects.  FIG.  2    shows the signaling flow of the basic conditional handover between a UE  202 , a source cell  204 , and a target cell  206 . The key idea is to configure a “lower” threshold for one or more measurement events, to trigger early measurement report to the serving cell. Then the serving cell  204  will prepare the target cell and forward the handover command to the UE with a “higher” threshold for the measurement event to increase the reliability of the handover command. When the “higher” threshold condition is met, the UE will trigger handover (synchronization to the target cell and a random access procedure) to the target cell  206 . One of the issues associated with handover failure (HOF) is the failure in delivery of the HO command. In conditional handover (e.g., as illustrated in  FIG.  2   ), the measurement report is triggered based on a lower threshold, therefore, the HO command delivery will be more reliable. 
     Referring to  FIG.  2   , at operation  208 , a measurement report is triggered based on a lower threshold for a measurement event. The measurement event, as well as the associated low threshold, can be configured prior to operation  208 , by the source cell  204 . At operation  210 , the source cell  204  can make a handover decision based on the received measurement report. At operation  212 , the source cell  204  communicates a handover request to the target cell  206 . The handover request can include a request for conditional handover based on a higher threshold (i.e., a threshold that is higher than the low threshold configured for the measurement report in operation  208 ). At operation  214 , the target cell  206  accepts the handover request. At operation  216 , the target cell  206  communicates a handover acknowledgment to the source cell  204 . The handover acknowledgment can include a conditional handover command including a high threshold for a measurement event (e.g., the measurement event used for triggering the measurement report in operation  208 ). At operation  218 , the source cell  204  communicates a conditional handover command (e.g., the conditional handover command received with the handover acknowledgment at operation  216 ) together with the high threshold to the UE  202 . At operation  220 , the UE  202  performs a measurement on the target cell  206  which satisfies the high threshold communicated with the conditional handover command. At operation  222 , synchronization and random access procedure can take place between the UE  202  and the target cell  206 . At operation  224 , the UE can communicate a handover completion message, such as RRC Connection Reconfiguration Complete message. 
     Observation 1: Conditional handover may increase the reliability of HO command delivery by early event triggering.  FIG.  2    illustrates a simpler case of conditional HO where there is only one target cell triggering the UE to send the measurement report, with the UE eventually triggering HO when the “higher” threshold is met.  FIG.  3    illustrates a different communication environment where more than one target cells triggered the UE to send the measurement report. 
       FIG.  3    illustrates a swimlane diagram of a conditional handover with more than one target cells, in accordance with some aspects.  FIG.  3    shows a communication sequence where multiple potential target cells were triggered by a “lower” threshold and hence measurement reports were sent by the UE. Multiple target cells preparation will be required along with multiple HO commands were sent to the UE. Therefore, more signaling overhead in conditional handover due to multiple measurement report, preparation, and HO commands may be used in connection with  FIG.  3   . 
       FIG.  3    shows conditional handover signaling flow  300  where multiple potential target cells (e.g., a first target cell  306  and a second target cell  308 ) may trigger the UE  302  to sends measurement reports to the source cell  304 . In conditional handover, a “lower” threshold is configured to the UE to trigger early measurement reporting. After the serving cell  304  reserves the resource (e.g., prepares the target cell), the HO command will be sent to the UE  302  along with a “higher” threshold configuration for one or more measurement events (which may be configured together with the “lower” threshold). Multiple HO commands may be sent to the UE due to multiple potential target cell satisfying the “lower” threshold. This results in multiple target cells preparation and, therefore, more signaling overhead in the air interface and the X2 interface due to communication of multiple measurement reports, preparation, and HO commands. 
     Referring to  FIG.  3   , at operation  310 , a measurement report (for the first target cell  306 ) is triggered based on a lower threshold for a measurement event. The measurement event, as well as the associated low threshold, can be configured prior to operation  310 , by the source cell  304 . More specifically, prior to operation  310 , the network configures a low threshold in measurement configuration along with the measurement event to the UE. At operation  310 , the UE sends the measurement report when the event is triggered. i.e. one or more cells satisfy the low threshold configuration. 
     At operation  312 , the source cell  304  can make a handover decision for handover to the first target cell  306  based on the received measurement report at operation  310 . 
     At operation  314 , the source cell  304  communicates a handover request to the first target cell  306 . The handover request can include a request for conditional handover based on a higher threshold (i.e., a threshold that is higher than the low threshold configured for the measurement report in operation  310 ). The serving cell  304  sends the early HO request to the target cell (e.g.,  306 ) to reserve resource to the UE. This signaling may include a conditional HO request to check if the target cell supports conditional HO (this feature is currently not supported in legacy HO). 
     At operation  316 , the first target cell  306  accepts the handover request. 
     At operation  318 , the first target cell  306  communicates a handover acknowledgment to the source cell  304 . The handover acknowledgment can include a conditional handover command including a high threshold for a measurement event (e.g., the measurement event used for triggering the measurement report in operation  310 ). 
     In some aspects, at operation  318 , the target cell (e.g.,  306 ) sends either a HO acknowledgment (ACK) or reject to the serving cell based on support of conditional HO. In case of HO ACK, signaling at operation  318  may include the following: a HO command including a RACH resource (contention-free RACH preamble); a timer to indicate how long the RACH resource can be valid; an offset to indicate when the UE may exit the conditional HO; a high threshold for the conditional handover to execute; and a time-to-trigger (TTT) parameter for this condition, where the measurement has to satisfy the high threshold for TTT amount of time. 
     At operation  320 , the source cell  304  communicates a conditional handover command (e.g., the conditional handover command received from the first target cell  306  with the handover acknowledgment at operation  318  is forwarded) together with the high threshold to the UE  302 . 
     Once the UE receives the conditional HO command at operation  320 , the UE maintains a connection with the source/serving cell  304 . If the high threshold is satisfied with the configured target cell, the UE disconnects with the serving cell and performs a RACH procedure to the target cell to complete the HO. If the timer expired in the HO command, the UE discards the HO command and the target cell releases the resources. If an exit condition is satisfied, the UE sends an exit indication to the serving cell for the configured target cell. 
     At operation  322 , a measurement report (for the second target cell  308 ) is triggered based on a lower threshold for a measurement event. The measurement event, as well as the associated low threshold, can be configured prior to operation  322 , by the source cell  304 . 
     At operation  324 , the source cell  304  can make a handover decision for handover to the second target cell  306  based on the received measurement report at operation  310 . 
     At operation  326 , the source cell  304  communicates a handover request to the second target cell  308 . The handover request can include a request for conditional handover based on a higher threshold (i.e., a threshold that is higher than the low threshold configured for the measurement report in operation  322 ). 
     At operation  328 , the second target cell  308  accepts the handover request. 
     At operation  330 , the second target cell  308  communicates a handover acknowledgment to the source cell  304 . The handover acknowledgment can include a conditional handover command including a high threshold for a measurement event (e.g., the measurement event used for triggering the measurement report in operation  322 ). 
     At operation  332 , the source cell  304  communicates a conditional handover command (e.g., the conditional handover command received from the second target cell  306  with the handover acknowledgment at operation  330 ) together with the high threshold to the UE  302 . 
     At operation  334 , the UE  302  performs a measurement on one or more of the target cell and determines that measurement in a configured measurement event for the first target cell  306  satisfies the high threshold communicated with the conditional handover command (e.g., at operation  332 ). 
     At operation  336 , synchronization and random access procedure can take place between the UE  302  and the first target cell  306 . At operation  338 , the UE  302  can communicate a handover completion message to the first target cell  306 , such as an RRC Connection Reconfiguration Complete message. 
     After operation  338 , the target cell  306  sends a HO complete message to the serving cell to indicate the HO is completed. The serving cell  304  sends resources release message to all other configured target cells so that they can release the resources they are holding for UE  302 . 
     Observation 2: Conditional HO increases both the air interface and the X2 interface signaling (between the cells) overhead due to the communication of multiple measurement reports, preparation (HO request and ACK) messaging, and HO commands. Additionally, conditional handover can increase the reliability of HO command delivery by early event triggering, conditional handover may be associated with a longer handover duration than a legacy HO, and conditional handover may reduce HOF rate (e.g., by providing more reliable HO command delivery) in tradeoff of increasing air interface and X2 signaling overhead. 
     Additional aspects that may be considered in connection with techniques discussed herein include whether the target cell may configure a contention-based RACH procedure (CBRA), which may reduce the conservation of the resources to the UE. The following options may be used to configure such contention-based RACH procedure.
         Option1: the target cell can configure only contention-free RACH procedure (CFRA) with no timer, which may be valid until UE handover success or other indication from the network.   Option2: the target cell can configure CFRA with a timer indicating how long it is valid, then the UE uses CBRA after that.   Option3: the target cell can configure CFRA with a timer; when the timer expires, the UE does not consider the target cell anymore, and the UE will not fall back to CBRA.       

     If the timer expired, the UE may exit conditional handover, or the UE may use contention-based RACH after the timer expired. In this case, the UE will only exit conditional handover based on the offset (exit condition). 
     In some aspects, multiple HO commands may be used based on the following options. 
     Option 1: the UE considers all HO commands sent to the UE. Option 2: the UE considers all HO commands sent to the UE with a timer, as long as the timer is valid. Option 3: the UE considers all HO commands until the target cell exits the measurement event. Option 4: the UE considers only the last HO command. Option 5: The network can indicate remove to a potential target cell in which the HO command has sent to the UE (release of HO command). 
       FIG.  4    illustrates events for conditional handover  400  and legacy handover  420  in a timeline, in accordance with some aspects. The conditional HO  400  may include the following operations: the UE sends a measurement report (MR) for cell  1  at operation  402 ; the UE sends an MR for cell  2  at operation  404 ; the network sends an HO command (for cell  1 ) to the UE at operation  406 ; the network sends an HO command (for cell  2 ) to the UE at operation  408 ; UE sends an MR for cell  3  at operation  410 ; the UE executes conditional HO to cell  2 . 
     The legacy HO  420  may include the following operations: upon an event trigger, the UE sends an MR to the network at operation  422 , the network sends a HO command to the UE at operation  424 , and the UE performs the HO to the target at operation  426 . 
       FIG.  4    shows that conditional handover triggers earlier measurement reporting by configuring a smaller offset/threshold (e.g., configure A3 offset=0 dB instead of 2 dB). A higher threshold (e.g., 2 dB) can be used to trigger the UE-based conditional handover. Therefore, the duration of the HO cycle is longer in conditional HO than in the legacy HO. 
     Observation 3: Conditional HO tends to have a longer handover duration than legacy HO. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Handover performance for conditional handover  
               
               
                 in compare to legacy handover 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Conditional 
                 Conditional  
               
               
                   
                   
                   
                 HO 
                 HO 
               
               
                   
                   
                 Legacy 
                 Trigger cond: 
                 Trigger cond: 
               
               
                   
                   
                 HO 
                 0 dB 
                 1 dB 
               
               
                   
                   
               
               
                   
                 HOF rate 
                 22% 
                 17% 
                 18% 
               
               
                   
                 # MR 
                 713 
                 2152 
                 1328 
               
               
                   
                 # HO command 
                 713 
                 2152 
                 1328 
               
               
                   
                 # X2 signaling 
                 1426 
                 4304 
                 2656 
               
               
                   
                 Time from first HO 
                 40 ms 
                 98 ms 
                 97 ms 
               
               
                   
                 command to HOS 
               
               
                   
                   
               
            
           
         
       
     
     Table 1 above shows the simulation performance result for conditional handover with different parameters setting we discussed above. The simulation results show the handover failure (HOF) rate is improved in conditional HO due to more reliable delivery of the HO command. However, conditional HO has more than double signaling overhead in measurement reporting and HO command. Similarly, X2 signaling exchange is also doubled. By increasing the triggering condition from 0 dB to 1 dB, the signaling overhead is reduced. This implies the signaling overhead is due to too early triggering but in a trade-off of a slight increase in the HOF rate. 
     Observation 4: Conditional HO reduces HOF rate in a trade-off of air interface and X2 signaling overhead. 
       FIG.  5    illustrates a block diagram of a communication device such as an evolved Node-B (eNB), a next generation Node-B (gNB), an access point (AP), a wireless station (STA), a mobile station (MS), or a user equipment (UE), in accordance with some aspects and to perform one or more of the techniques disclosed herein. In alternative aspects, the communication device  500  may operate as a standalone device or may be connected (e.g., networked) to other communication devices. 
     Circuitry (e.g., processing circuitry) is a collection of circuits implemented in tangible entities of the device  500  that include hardware (e.g., simple circuits, gates, logic, etc.). Circuitry membership may be flexible over time. Circuitries include members that may, alone or in combination, perform specified operations when operating. In an example, the hardware of the circuitry may be immutably designed to carry out a specific operation (e.g., hardwired). In an example, the hardware of the circuitry may include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) including a machine-readable medium physically modified (e.g., magnetically, electrically, moveable placement of invariant massed particles, etc.) to encode instructions of the specific operation. 
     In connecting the physical components, the underlying electrical properties of a hardware constituent are changed, for example, from an insulator to a conductor or vice versa. The instructions enable embedded hardware (e.g., the execution units or a loading mechanism) to create members of the circuitry in hardware via the variable connections to carry out portions of the specific operation when in operation. Accordingly, in an example, the machine-readable medium elements are part of the circuitry or are communicatively coupled to the other components of the circuitry when the device is operating. In an example, any of the physical components may be used in more than one member of more than one circuitry. For example, under operation, execution units may be used in a first circuit of a first circuitry at one point in time and reused by a second circuit in the first circuitry, or by a third circuit in a second circuitry at a different time. Additional examples of these components with respect to the device  500  follow. 
     In some aspects, the device  500  may operate as a standalone device or may be connected (e.g., networked) to other devices. In a networked deployment, the communication device  500  may operate in the capacity of a server communication device, a client communication device, or both in server-client network environments. In an example, the communication device  500  may act as a peer communication device in peer-to-peer (P2P) (or other distributed) network environment. The communication device  500  may be a UE, eNB, PC, a tablet PC, a STB, a PDA, a mobile telephone, a smartphone, a web appliance, a network router, switch or bridge, or any communication device capable of executing instructions (sequential or otherwise) that specify actions to be taken by that communication device. Further, while only a single communication device is illustrated, the term “communication device” shall also be taken to include any collection of communication devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), and other computer cluster configurations. 
     Examples, as described herein, may include, or may operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities (e.g., hardware) capable of performing specified operations and may be configured or arranged in a certain manner. In an example, circuits may be arranged (e.g., internally or with respect to external entities such as other circuits) in a specified manner as a module. In an example, the whole or part of one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware processors may be configured by firmware or software (e.g., instructions, an application portion, or an application) as a module that operates to perform specified operations. In an example, the software may reside on a communication device-readable medium. In an example, the software, when executed by the underlying hardware of the module, causes the hardware to perform the specified operations. 
     Accordingly, the term “module” is understood to encompass a tangible entity, be that an entity that is physically constructed, specifically configured (e.g., hardwired), or temporarily (e.g., transitorily) configured (e.g., programmed) to operate in a specified manner or to perform part or all of any operation described herein. Considering examples in which modules are temporarily configured, each of the modules need not be instantiated at any one moment in time. For example, where the modules comprise a general-purpose hardware processor configured using software, the general-purpose hardware processor may be configured as respective different modules at different times. The software may accordingly configure a hardware processor, for example, to constitute a particular module at one instance of time and to constitute a different module at a different instance of time. 
     Communication device (e.g., UE)  500  may include a hardware processor  502  (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory  504 , a static memory  506 , and mass storage  507  (e.g., hard drive, tape drive, flash storage, or other block or storage devices), some or all of which may communicate with each other via an interlink (e.g., bus)  508 . 
     The communication device  500  may further include a display device  510 , an alphanumeric input device  512  (e.g., a keyboard), and a user interface (UI) navigation device  514  (e.g., a mouse). In an example, the display device  510 , input device  512  and UI navigation device  514  may be a touchscreen display. The communication device  500  may additionally include a signal generation device  518  (e.g., a speaker), a network interface device  520 , and one or more sensors  521 , such as a global positioning system (GPS) sensor, compass, accelerometer, or another sensor. The communication device  500  may include an output controller  528 , such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.). 
     The storage device  507  may include a communication device-readable medium  522 , on which is stored one or more sets of data structures or instructions  524  (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. In some aspects, registers of the processor  502 , the main memory  504 , the static memory  506 , and/or the mass storage  507  may be, or include (completely or at least partially), the device-readable medium  522 , on which is stored the one or more sets of data structures or instructions  524 , embodying or utilized by any one or more of the techniques or functions described herein. In an example, one or any combination of the hardware processor  502 , the main memory  504 , the static memory  506 , or the mass storage  516  may constitute the device-readable medium  522 . 
     As used herein, the term “device-readable medium” is interchangeable with “computer-readable medium” or “machine-readable medium”. While the communication device-readable medium  522  is illustrated as a single medium, the term “communication device-readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) configured to store the one or more instructions  524 . The term “communication device-readable medium” is inclusive of the terms “machine-readable medium” or “computer-readable medium”, and may include any medium that is capable of storing, encoding, or carrying instructions (e.g., instructions  524 ) for execution by the communication device  500  and that cause the communication device  500  to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting communication device-readable medium examples may include solid-state memories and optical and magnetic media. Specific examples of communication device-readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; Random Access Memory (RAM); and CD-ROM and DVD-ROM disks. In some examples, communication device-readable media may include non-transitory communication device-readable media. In some examples, communication device-readable media may include communication device-readable media that is not a transitory propagating signal. 
     The instructions  524  may further be transmitted or received over a communications network  526  using a transmission medium via the network interface device  520  utilizing any one of a number of transfer protocols. In an example, the network interface device  520  may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network  526 . In an example, the network interface device  520  may include a plurality of antennas to wirelessly communicate using at least one of single-input-multiple-output (SIMO), MIMO, or multiple-input-single-output (MISO) techniques. In some examples, the network interface device  520  may wirelessly communicate using Multiple User MIMO techniques. 
     The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the communication device  500 , and includes digital or analog communications signals or another intangible medium to facilitate communication of such software. In this regard, a transmission medium in the context of this disclosure is a device-readable medium. 
     Although an aspect has been described with reference to specific exemplary aspects, it will be evident that various modifications and changes may be made to these aspects without departing from the broader scope of the present disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various aspects is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

Metadata:
Filing Date: 20190911
Publication Date: 20240521
Grant Date: 20240521
Priority Date: 20180920
Inventors: YIU, Candy
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W36/362", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/00838", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/00837", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L5/0053", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0058", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/0841", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/362", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/0058", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/00838", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0058", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0053", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/0841", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 69888037