PRIORITY CLAIM

[0001] This application claims the benefit of priority to the United States

Provisional Patent Application Serial No. 62/737,512, filed September 27, 2018, and entitled“DATA FORWARDING HANDLING FOR CONDITIONAL HANDOVER,” which provisional patent applications is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] Aspects pertain to wireless communications. Some aspects relate to wireless networks including 3 GPP (Third Generation Partnership Project) networks, 3 GPP LTE (Long Term Evolution) networks, 3 GPP 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

[0003] Mobile communications have evolved significantly from early voice systems to today’s highly sophisticated integrated communication platform. With the increase in different types of devices communicating with various network devices, usage of 3 GPP 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 3 GPP LTE-Advanced with additional potential new radio access technologies (RATs) to enrich people’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 (mm Wave) frequency, can be beneficial due to their high bandwidth.

[0004] 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.

[0005] Further enhanced operation of LTE system s in the licensed as well as unlicensed spectrum is expected in future releases and 5G systems. Such enhanced operations can include techniques for data forwarding handling for conditional handover in wireless networks.

BRIEF DESCRIPTION OF THE FIGURES

[0006] 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.

[0007] FIG. 1 A illustrates an architecture of a network, in accordance with some aspects.

[0008] FIG. 1B and FIG. 1C illustrate a non-roaming 5G system architecture in accordance with some aspects.

[0009] FIG. 2 illustrates a swimlane diagram of a conditional handover, in accordance with some aspects.

[0010] FIG. 3 illustrates a swimlane diagram of a conditional handover with more than one target cells and options for data forwarding, in accordance with some aspects.

[0011] FIG. 4 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

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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 (ESA) 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).

[0017] Aspects described herein can also be applied to different Single

Carrier or OFDM flavors (CP-OFDM, SC-FDMA, SC-OFDM, filter bank-based multi carrier (FBMC), OF DMA, etc.) and in particular 3 GPP NR (New Radio) by allocating the OFDM carrier data bit vectors to the corresponding symbol resources.

[0018] In some aspects, any of the UEs 101 and 102 can comprise an

Intemet-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.

[0019] In some aspects, any of the UEs 101 and 102 can include enhanced MTC (eMTC) UEs or further enhanced MTC (FeMTC) UEs.

[0020] The UEs 101 and 102 may be configured to connect, e.g., communi cati vely couple, with a radio access network (RAN) 110. The RAN 1 10 may be, for example, an Evolved Universal Mobile T el ecommuni cati on s 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 Tel ecom m uni cati ons System (UMTS) protocol, a 3 GPP Long Term Evolution (LTE) protocol, a fifth-generation (5G) protocol, a New Radio (NR) protocol, and the like.

[0021] 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 si delink 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).

[0022] 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).

[0023] 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 1 12 can be transmission/reception points (TRPs) In instances when the communication nodes 111 and 112 are NodeBs (e.g., eNBs or gNBs), one or m ore 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 1 1 1, and one or more RAN nodes for providing femtocells or pi cocells (e.g., cells having smaller coverage areas, smaller user capacity, or higher bandwidth compared to macrocells), e.g., low power (LP) RAN node 112.

[0024] Any of the R AN nodes 1 1 1 and 1 12 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 1 12 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 1 11 and/or 112 can be a new generation Node-B (gNB), an evolved node-B (eNB), or another type of RAN node.

[0025] The RAN 1 10 is shown to be communi cati v el y coupled to a core network (CN) 120 via an Sl 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 S l interface 1 13 is split into two parts: the Sl-U interface 1 14, which carries traffic data between the RAN nodes 1 1 1 and 112 and the serving gateway (S-GW) 122, and the Sl -mobility management entity (MME) interface 115, which is a signaling interface between the RAN nodes 1 1 1 and 112 and MMEs 121

[0026] 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' handling of communi cati on 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. [0027] The S-GW 122 may terminate the Sl 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-3 GPP mobility. Other responsibilities of the S-GW 122 may include a lawful intercept, charging, and some policy enforcement.

[0028] 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, P IT sessions, group communication sessions, social networking services, etc.) for the UEs 101 and 102 via the CN 120.

[0029] 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'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'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.

[0030] 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). [0031] 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 communi cati vel y 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.

[0032] In some aspects, the NG system architecture can use reference points between various nodes as provided by 3 GPP 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.

[0033] FIG. 1B illustrates a non-roaming 5G system architecture in accordance with some aspects. Referring to FIG. IB, there is illustrated a 5G system architecture 140B 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 140B 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 sendees. 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).

[0034] In some aspects, the 5G system architecture 140B includes an IP multimedia subsystem (IMS) 168B as well as a plurality of IP multimedia core network subsystem entities, such as call session control functions (CSCFs).

More specifically, the IMS 168B includes a CSCF, which can act as a proxy CSCF (P-CSCF) 162BE, a serving CSCF (S-CSCF) 164B, an emergency CSCF (E-CSCF) (not illustrated in FIG. 1B), or interrogating CSCF (I-CSCF) 166B. The P-CSCF 162B can be configured to be the first contact point for the UE 102 within the IM subsystem (IMS) 168B. The S-CSCF 164B 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 166B can be configured to function as the contact point within an operator's network for all IMS connections destined to a subscriber of that network operator, or a roaming subscriber currently located within that network operator's service area. In some aspects, the I-CSCF 166B can be connected to another IP multimedia network 170E, e.g. an IMS operated by a different network operator.

[0035] In some aspects, the UDMZHSS 146 can be coupled to an application server 160E, which can include a telephony application server (TAS) or another application server (AS). The AS 160B can be coupled to the IMS 168B via the S-CSCF 164B or the I-CSCF 166B.

[0036] A reference point representation shows that interaction can exist between corresponding NF services. For example, FIG. IB illustrates the following reference points: Nl (between the UE 102 and the AMF 132), N2 (between the RAN 110 and the AMF 132), N3 (between the RAN 110 and the UPF 134), N4 (between the SMF 136 and the UPF 134), N5 (between the PCF 148 and the AF 150, not shown), N6 (between the UPF 134 and the DN 152),

N7 (between the SMF 136 and the PCF 148, not shown), N8 (between the UDM 146 and the AMF 132, not shown), N9 (between two UPFs 134, not shown),

N10 (between the UDM 146 and the SMF 136, not shown), Nl 1 (between the AMF 132 and the SMF 136, not shown), N12 (between the AUSF 144 and the AMF 132, not shown), N13 (between the AUSF 144 and the UDM 146, not shown), N14 (between two AMFs 132, not shown), N15 (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), N16 (between two SMFs, not shown), and N22 (between AMF 132 and NSSF 142, not shown). Other reference point representations not shown in FIG. IE can also be used.

[0037] FIG. 1C illustrates a 5G system architecture 140C and a service- based representation. In addition to the network entities illustrated in FIG. 1B, system architecture 140C 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.

[0038] In some aspects, as illustrated in FIG. 1C, 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 140C can include the following service- based interfaces: Namf 158H (a service-based interface exhibited by the AMF 132), Nsmf 1581 (a service-based interface exhibited by the SMF 136), Nnef 158B (a service-based interface exhibited by the NEF 154), Npcf 158D (a service-based interface exhibited by the PCF 148), a Nudm 158E (a service- based interface exhibited by the UDM 146), Naf 158F (a service-based interface exhibited by the AF 150), Nnrf 158C (a service-based interface exhibited by the NRF 156), Nnssf 158 A (a service-based interface exhibited by the NSSF 142), Nausf 158G (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.

[0039] In some aspects associated with conditional handover (FIO), multiple potential target cells can be prepared among which the UE is configured to choose a final target cell for FIO. This framework impacts on legacy data forwarding. In LTE, the source freezes downlink (DL) / uplink (UL) communications with the UE and initiates data forwarding at any time after sending RIIC Reconfiguration including a HO command (CMD) to the UE (as the target node to which data can be forwarded is already decided and known to the source cell). However, in conditional HO, multiple candidates (e.g., multiple target cells) over multiple nodes can be prepared (meaning that HO preparation and HO CMD configuration to the UE are done for each candidate target cell), where the final target cell is chosen as the one that the UE successfully attaches to. As a result, the source cell could lack knowledge on which target cell the UE has attached to and, consequently, the source cell may not be able to follow the legacy data forwarding behavior after the source cell communicates the HO CMD.

[0040] Techniques discussed herein can be used to enable data forwarding when the conditional HO is used and multiple potential target cells over one or multiple nodes are prepared for a UE (e.g., as illustrated and discussed in connection with FIG. 3). More specifically, the following techniques may be used to enable data forwarding in a conditional HO:

[0041] (a) In some aspects, the final target node sends a notification to the source when the UE has successfully attached so that the source can initiate data forwarding: a straightforward solution with impacting NW signalling only (no UE impact) but there could be some interruption as data may not be ready (not forwarded yet) on the target side.

[0042] (b) In some aspects, the source cell (also referred to as the source) performs data forwarding to potential target nodes: a brute-force solution applying the legacy forwarding behavior to each potential target (no stage-3 impact foreseen), but waste of X2-U or Xn-U resources is expected as data forwarded to non-selected target node(s) may become useless. In some aspects, forwarding can be performed to some candidate target cells, not necessarily all target cells.

[0043] (c) In some aspects, the UE informs to the source“which target” it will connect to before di sconnecting from the source and attaching to the target: a UE-based solution that enables the source to follow the legacy data forwarding behavior as the source can know to which target node it should forward data to before the UE is disconnected. This solution may be unreliable as the signal quality between the UE and the source cell is expected to be poor around the time when the UE disconnects from the source. [0044] (d) In some aspects, both the final target node and the UE signal the source (this technique is a hybrid of techniques (a) and (c)). In some aspects, at least the final target will signal to the source with the tradeoff of delay. But in aspects when the UE signals the source, the delay may be minimalized.

[0045] (e) In some aspects, the source performs data forwarding to some target nodes based on information from the UE before disconnecting from the source and attaching to the target (a hybrid of techniques (b) and (c) that could help the source to narrow down the nodes to forward data to). Additional information regarding techniques (a) - (e) is discussed in connection with FIG.

3.

[0046] 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 the deli very 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.

[0047] 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.

[0048] In some aspects, 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.

[0049] FIG. 3 illustrates a swimlane diagram of a conditional handover with more than one target cells and options for data forwarding, 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.

[0050] 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 or Xn interface due to communication of multiple measurement reports, preparation, and HO commands.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] At operation 316, the first target cell 306 accepts the handover request.

[0055] 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). [0056] In some aspects, at operation 318, the target cell (e.g., 306) sends either an HO acknowledgment (ACK) or reject to the serving cell based on the 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 (TXT) parameter for this condition, where the measurement has to satisfy the high threshold for TTT amount of time.

[0057] 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.

[0058] 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 tim er 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.

[0059] 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.

[0060] At operation 324, the source cell 304 can make a handover decision for handover to the second target cell 308 based on the received measurement report at operation 310.

[0061] 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). [0062] At operation 328, the second target cell 308 accepts the handover request.

[0063] 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).

[0064] At operation 332, the source cell 304 communicates a conditional handover command (e.g., the conditional handover command received from the second target cell 308 with the handover acknowledgment at operation 330) together with the high threshold to the UE 302.

[0065] 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 320).

[0066] 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.

[0067] After operation 338, the target cell 306 sends an HO complete message to the serving cell to indicate the HO is completed. The serving cell 304 sends a resources release message to all other configured target cells so that they can release the resources they are holding for UE 302.

[0068] In the first aspect of data forwarding in connection with conditional HO, the final target node (cell) sends a notification to the source cell when the UE has successfully attached so that the source cell can initiate data forwarding. For example, after operation 338, at operation 340, the final target cell (e.g., 306) communicates an HO success indication to the source cell 304 (e.g., indicating the UE has completed the HO and has attached to the target cell 306). At operation 342, the source cell 304 can perform data forwarding to the target cell 306 of any UE data received from the UE (e.g., UL data that has been received but held at the source cell after communication of the HO command at operation 332) or DL data for the UE (e.g., data that has been held at the source cell for communication to the UE). [0069] This solution is to let the final target cell notify the source cell to which node the source should forward data to. The target can indicate the source as soon as the UE successfully attaches, possibly before or at the same time when initiating path switch, to minimize service interruption. This technique has no UE impact. Even if the notification from the target cell happens right after the UE attaches, there could be some interruption as data may not be ready (not forwarded yet) on the target side. The target cell can use X2AP or XnAP signaling to notify the source cell.

[0070] In the second aspect of data forwarding in connection with conditional HO, the source cell 304 performs data forwarding to potential target nodes. The source cell may perform the legacy forwarding behavior to each potential target nodes in a brute-force way since the source cell does not know exactly which target cell the UE is going to attach to. For example, after operation 320, the source cell can perform data forwarding of UE’s UL or DL data to the target cell 306 (which is known to the source cell), at operation 344. After operation 332, the source cell 304 can further perform data forwarding to target cell 308 (at operation 348).

[0071] This technique has no UE or network impacts. The data forwarding can be adapted to each potential target based on admission result. In some aspects, no interruption may be expected because the source cell in effect follows the legacy data forwarding behavior to each potential target cell. In some aspects, the source cell may not necessarily need to forward the data to all candidates; the source cell can forward data to some of the target cell candidates instead. This technique may extensively use X2-U or Xn-U resources as data is forwarded to the non-selected target node(s), which data becomes useless when forwarding takes place to non-selected target nodes.

[0072] In the third aspect of data forwarding in connection with conditional HO, the UE 302 informs to the source cell 304 which target cell the UE will connect to, before disconnecting from the source cell and attaching to the target cell. For example, after the measurements are performed at operation 334 (leading to the selection of target cell 306), the UE notifies the source cell 304 of the selection of target cell 306 (at operation 350). The source cell 304, at operation 352, then performs data forwarding to the target cell (306) indicated by the UE at operation 350. [0073] This technique is based on having the UE inform the source cell of the final target cell that the UE is going to attach to, before disconnecting from the source cell. This technique enables the source cell to follow the legacy data forwarding behavior as the source cell can know to which target cell it should forward the data before the UE is disconnected.

[0074] This technique has no network impact, and no interruption may be expected as the source cell can follow the legacy data forwarding behavior. The signal quality between the UE and the source cell may be poor around the time when the UE disconnects from the source cell, thus in some aspects, the UE indication may fail to be delivered. RRC signaling from the UE may be used to inform the source about the final target cell or node.

[0075] In the fourth aspect of data forwarding in connection with conditional HO, both the final target node and the UE signal the source cell.

This technique is a hybrid of the first and third techniques discussed above, because, sometimes, the UE may not have enough power (or may experience high interference) to send a message to the source cell during the handover. In this case, at least the final target cell will signal to the source cell (with the tradeoff of delay). In aspects when the signaling is performed by the UE, the delay will be minimized.

[0076] In the fifth aspect of data forwarding in connection with conditional HO, the source cell performs data forwarding to potential target cells based on information from the UE, received at the source cell before the UE disconnects from the source cell and attaches to the target cell. For example, the UE may send information on target cells that are highly likely to be selected for handover (e.g., based on multiple cell measurements of the target cells or another criteria), and the source cell may forward the data to the indicated likely target cells (which may be a subset of all the candidate target cells). This technique is a hybrid of the second and third techniques above, and may help the source cell to narrow down the nodes to forward data to, among all potential target nodes, based on the information from the UE (e.g., measurement-b ased information for the target cells), which information the UE can be configured to send before disconnecting from the source cell and attaching to the target cell.

[0077] In some aspects, an apparatus to be employed as an evolved

Node-B (eNB) or a next generation Node-B (gNB) (i.e., a source node) inter- connecting an eNB or a gNB (i.e., a potential target node) via X2 or Xn interfaces, includes means to support conditional HO and data forwarding for a specific HE. The source node performs data forwarding to all or some potential target nodes, possibly based on information provided by the HE or for which the HE can be configured to send (e g., measurement-based) before disconnecting from the source and attaching to a target node. The source node initiates data forwarding, either upon receiving notification signaling from the target node when the HE has successfully attached or upon receiving signaling from the HE that indicates which target node the LIE will connect to before the HE is disconnected from the source and attaches to the target.

[0078] FIG. 4 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 (HE), in accordance with some aspects and to perform one or more of the techniques disclosed herein. In alternative aspects, the communication device 400 may operate as a standalone device or may be connected (e.g., networked) to other communication devices.

[0079] Circuitry (e.g., processing circuitry) is a collection of circuits implemented in tangible entities of the device 400 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.

[0080] In connecting the physical components, the underlying electrical properties of a hardware constituent are changed, for example, from an insul ator to a conductor or vice versa. The instructions enable embedded hardware (e.g., the execution units or a l oading 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 400 follow.

[0081] In some aspects, the device 400 may operate as a standalone device or may be connected (e.g., networked) to other devices. In a networked deployment, the communication device 400 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 400 may act as a peer communication device in peer-to-peer (P2P) (or other distributed) network environment. The communication device 400 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.

[0082] 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.

[0083] 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 the 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 m odul e at a different instance of time.

[0084] Communication device (e.g., IJE) 400 may include a hardware processor 402 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 404, a static memory 406, and mass storage 407 (e.g., hard drive, tape drive, flash storage, or other block or storage devi ces), some or all of which may communicate with each other via an interlink (e.g., bus) 408.

[0085] The communication device 400 may further include a display device 410, an alphanumeric input device 412 (e.g., a keyboard), and a user interface (UI) navigation device 414 (e.g., a mouse). In an example, the display device 410, input device 412 and UI navigation device 414 may be a touchscreen display. The communication device 400 may additionally include a signal generation device 418 (e.g., a speaker), a network interface device 420, and one or more sensors 421, such as a global positioning system (GPS) sensor, compass, accelerometer, or another sensor. The communication device 400 may include an output controller 428, 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.).

[0086] The storage device 407 may include a communication device- readable medium 422, on which is stored one or more sets of data structures or instructi ons 424 (e.g., software) embodying or utili zed by any one or more of the techniques or functions described herein. In some aspects, registers of the processor 402, the main memory 404, the static memory 406, and/or the mass storage 407 may be, or include (completely or at least partially), the device- readable medium 422, on which is stored the one or more sets of data structures or instructions 424, 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 402, the main memory 404, the static memory 406, or the mass storage 416 may constitute the device-readable medium 422.

[0087] As used herein, the term "device-readable medium" is

interchangeable with“computer-readable medium” or“machine-readable medium”. While the communication device-readable medium 422 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 424. 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 424) for execution by the communication device 400 and that cause the communication device 400 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 n on-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.

[0088] The instructions 424 may further be transmitted or received over a communications network 426 using a transmission medium via the network interface device 420 utilizing any one of a number of transfer protocols. In an example, the network interface device 420 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 426. In an example, the network interface device 420 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 420 may wirelessly communicate using Multiple User MIMO techniques.

[0089] 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 400, 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.

[0090] 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.