Patent Description:
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 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 (<NUM>) wireless systems are forthcoming and are expected to enable even greater speed, connectivity, and usability. Next generation <NUM> networks (or NR networks) are expected to increase throughput, coverage, and robustness and reduce latency and operational and capital expenditures. <NUM>-NR networks will continue to evolve based on 3GPP 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 (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 <NUM> systems. Such enhanced operations can include techniques for conditional handover in wireless networks.

<CIT> describes a wireless communication device configured to receive a command that commands the device to perform a link switch from a source link to a target link responsive to fulfillment of a condition.

<CIT> describes a method performed by a wireless device for handover, comprising receiving a first handover message from a source network node associated with a source cell which comprises an identification of a target cell and access information associated with the target cell, wherein the target cell is different than the source cell and comprises one or more beams.

<NPL> describes various aspects of conditional handovers for 3GPP networks.

<CIT> describes an apparatus of a user equipment (UE) that comprises one or more baseband processors to decode a conditional handover command from a serving cell for the UE to connect with a target cell, and to evaluate a condition before executing the handover command. <CIT> was published after the priority date of the present application and therefore is relevant only when assessing the novelty of the present application.

In the figures, which are not necessarily drawn to scale, like numerals may describe similar components in different views. The figures illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document.

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 within the scope of the invention defined by those claims.

<FIG> illustrates an architecture of a network in accordance with some aspects. The network 140A is shown to include user equipment (UE) <NUM> and UE <NUM>. The UEs <NUM> and <NUM> 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 <NUM> and <NUM> can be collectively referred to herein as UE <NUM>, and UE <NUM> 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 140A 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 <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and further frequencies and Spectrum Access System (SAS) in <NUM>-<NUM> 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 <NUM> and <NUM> 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 <NUM> and <NUM> 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 <NUM> and <NUM> can include enhanced MTC (eMTC) UEs or further enhanced MTC (FeMTC) UEs.

The UEs <NUM> and <NUM> may be configured to connect, e.g., communicatively couple, with a radio access network (RAN) <NUM>. The RAN <NUM> 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 <NUM> and <NUM> utilize connections <NUM> and <NUM>, respectively, each of which comprises a physical communications interface or layer (discussed in further detail below); in this example, the connections <NUM> and <NUM> 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 (<NUM>) protocol, a New Radio (NR) protocol, and the like.

In an aspect, the UEs <NUM> and <NUM> may further directly exchange communication data via a ProSe interface <NUM>.

The connection <NUM> can comprise a local wireless connection, such as, for example, a connection consistent with any IEEE <NUM> protocol, according to which the AP <NUM> can comprise a wireless fidelity (WiFi®) router.

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 <NUM> and <NUM> can be transmission/reception points (TRPs). In instances when the communication nodes <NUM> and <NUM> are NodeBs (e.g., eNBs or gNBs), one or more TRPs can function within the communication cell of the NodeBs.

In some aspects, any of the RAN nodes <NUM> and <NUM> can fulfill various logical functions for the RAN <NUM> 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 <NUM> and/or <NUM><NUM> can be a new generation Node-B (gNB), an evolved node-B (eNB), or another type of RAN node.

The RAN <NUM> is shown to be communicatively coupled to a core network (CN) <NUM> via an S1 interface <NUM>. In aspects, the CN <NUM> 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 <FIG>). In this aspect, the S1 interface <NUM> is split into two parts: the S1-U interface <NUM>, which carries traffic data between the RAN nodes <NUM> and <NUM> and the serving gateway (S-GW) <NUM>, and the S1-mobility management entity (MME) interface <NUM>, which is a signaling interface between the RAN nodes <NUM> and <NUM> and MMEs <NUM>.

In this aspect, the CN <NUM> comprises the MMEs <NUM>, the S-GW <NUM>, the Packet Data Network (PDN) Gateway (P-GW) <NUM>, and a home subscriber server (HSS) <NUM>.

Other responsibilities of the S-GW <NUM> may include a lawful intercept, charging, and some policy enforcement.

The P-GW <NUM> can also communicate data to other external networks 131A, which can include the Internet, IP multimedia subsystem (IPS) network, and other networks. In this aspect, the P-GW <NUM> is shown to be communicatively coupled to an application server <NUM> via an IP interface <NUM>.

Policy and Charging Rules Function (PCRF) <NUM> is the policy and charging control element of the CN <NUM>. 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).

In some aspects, the communication network 140A 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 <NUM> and a <NUM> network core (5GC) <NUM>. The NG-RAN <NUM> can include a plurality of nodes, such as gNBs and NG-eNBs. The core network <NUM> (e.g., a <NUM> 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) <NUM> (e.g., V15. <NUM>, <NUM>-<NUM>). 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 <NUM> architecture.

<FIG> illustrates a non-roaming <NUM> system architecture in accordance with some aspects. Referring to <FIG>, there is illustrated a <NUM> system architecture 140B in a reference point representation. More specifically, UE <NUM> can be in communication with RAN <NUM> as well as one or more other <NUM> core (5GC) network entities. The <NUM> system architecture 140B includes a plurality of network functions (NFs), such as access and mobility management function (AMF) <NUM>, session management function (SMF) <NUM>, policy control function (PCF) <NUM>, application function (AF) <NUM>, user plane function (UPF) <NUM>, network slice selection function (NSSF) <NUM>, authentication server function (AUSF) <NUM>, and unified data management (UDM)/home subscriber server (HSS) <NUM>. The UPF <NUM> can provide a connection to a data network (DN) <NUM>, which can include, for example, operator services, Internet access, or third-party services. The AMF <NUM> can be used to manage access control and mobility and can also include network slice selection functionality. The SMF <NUM> can be configured to set up and manage various sessions according to network policy. The UPF <NUM> can be deployed in one or more configurations according to the desired service type. The PCF <NUM> can be configured to provide a policy framework using network slicing, mobility management, and roaming (similar to PCRF in a <NUM> communication system). The UDM can be configured to store subscriber profiles and data (similar to an HSS in a <NUM> communication system).

In some aspects, the <NUM> 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>), or interrogating CSCF (I-CSCF) 166B. The P-CSCF 162B can be configured to be the first contact point for the UE <NUM> 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.

In some aspects, the UDM/HSS <NUM> 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.

A reference point representation shows that interaction can exist between corresponding NF services. For example, <FIG> illustrates the following reference points: N1 (between the UE <NUM> and the AMF <NUM>), N2 (between the RAN <NUM> and the AMF <NUM>), N3 (between the RAN <NUM> and the UPF <NUM>), N4 (between the SMF <NUM> and the UPF <NUM>), N5 (between the PCF <NUM> and the AF <NUM>, not shown), N6 (between the UPF <NUM> and the DN <NUM>), N7 (between the SMF <NUM> and the PCF <NUM>, not shown), N8 (between the UDM <NUM> and the AMF <NUM>, not shown), N9 (between two UPFs <NUM>, not shown), N10 (between the UDM <NUM> and the SMF <NUM>, not shown), N11 (between the AMF <NUM> and the SMF <NUM>, not shown), N12 (between the AUSF <NUM> and the AMF <NUM>, not shown), N13 (between the AUSF <NUM> and the UDM <NUM>, not shown), N14 (between two AMFs <NUM>, not shown), N15 (between the PCF <NUM> and the AMF <NUM> in case of a non-roaming scenario, or between the PCF <NUM> and a visited network and AMF <NUM> in case of a roaming scenario, not shown), N16 (between two SMFs, not shown), and N22 (between AMF <NUM> and NSSF <NUM>, not shown). Other reference point representations not shown in FIG. 1E can also be used.

<FIG> illustrates a <NUM> system architecture 140C and a service-based representation. In addition to the network entities illustrated in <FIG>, system architecture 140C can also include a network exposure function (NEF) <NUM> and a network repository function (NRF) <NUM>. In some aspects, <NUM> 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>, 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, <NUM> system architecture 140C can include the following service-based interfaces: Namf <NUM> (a service-based interface exhibited by the AMF <NUM>), Nsmf 158I (a service-based interface exhibited by the SMF <NUM>), Nnef 158B (a service-based interface exhibited by the NEF <NUM>), Npcf 158D (a service-based interface exhibited by the PCF <NUM>), a Nuclm 158E (a service-based interface exhibited by the UDM <NUM>), Naf 158F (a service-based interface exhibited by the AF <NUM>), Nnrf 158C (a service-based interface exhibited by the NRF <NUM>), Nnssf 158A (a service-based interface exhibited by the NSSF <NUM>), Nausf <NUM> (a service-based interface exhibited by the AUSF <NUM>). Other service-based interfaces (e.g., Nudr, N5g-eir, and Nudsf) not shown in <FIG> 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 <NUM> (i.e., relaxed requirements could be considered) and improve robustness during handover.

<FIG> illustrates a swimlane diagram <NUM> of a conditional handover, in accordance with some aspects. <FIG> shows the signaling flow of the basic conditional handover between a UE <NUM>, a source cell <NUM>, and a target cell <NUM>. 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 <NUM> 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 <NUM>. 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>), the measurement report is triggered based on a lower threshold, therefore, the HO command delivery will be more reliable.

Referring to <FIG>, at operation <NUM>, 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 <NUM>, by the source cell <NUM>. At operation <NUM>, the source cell <NUM> can make a handover decision based on the received measurement report. At operation <NUM>, the source cell <NUM> communicates a handover request to the target cell <NUM>. 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 <NUM>). At operation <NUM>, the target cell <NUM> accepts the handover request. At operation <NUM>, the target cell <NUM> communicates a handover acknowledgment to the source cell <NUM>. 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 <NUM>). At operation <NUM>, the source cell <NUM> communicates a conditional handover command (e.g., the conditional handover command received with the handover acknowledgment at operation <NUM>) together with the high threshold to the UE <NUM>. At operation <NUM>, the UE <NUM> performs a measurement on the target cell <NUM> which satisfies the high threshold communicated with the conditional handover command. At operation <NUM>, synchronization and random access procedure can take place between the UE <NUM> and the target cell <NUM>. At operation <NUM>, the UE can communicate a handover completion message, such as RRC Connection Reconfiguration Complete message.

Observation <NUM>: Conditional handover may increase the reliability of HO command delivery by early event triggering. <FIG> 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> illustrates a different communication environment where more than one target cells triggered the UE to send the measurement report.

<FIG> illustrates a swimlane diagram of a conditional handover with more than one target cells, in accordance with some aspects. <FIG> 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>.

<FIG> shows conditional handover signaling flow <NUM> where multiple potential target cells (e.g., a first target cell <NUM> and a second target cell <NUM>) may trigger the UE <NUM> to sends measurement reports to the source cell <NUM>. In conditional handover, a "lower" threshold is configured to the UE to trigger early measurement reporting. After the serving cell <NUM> reserves the resource (e.g., prepares the target cell), the HO command will be sent to the UE <NUM> 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>, at operation <NUM>, a measurement report (for the first target cell <NUM>) 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 <NUM>, by the source cell <NUM>. More specifically, prior to operation <NUM>, the network configures a low threshold in measurement configuration along with the measurement event to the UE. At operation <NUM>, the UE sends the measurement report when the event is triggered. i.e. one or more cells satisfy the low threshold configuration.

At operation <NUM>, the source cell <NUM> can make a handover decision for handover to the first target cell <NUM> based on the received measurement report at operation <NUM>.

At operation <NUM>, the source cell <NUM> communicates a handover request to the first target cell <NUM>. 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 <NUM>). The serving cell <NUM> sends the early HO request to the target cell (e.g., <NUM>) 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 <NUM>, the first target cell <NUM> accepts the handover request.

At operation <NUM>, the first target cell <NUM> communicates a handover acknowledgment to the source cell <NUM>. 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 <NUM>).

In some aspects, at operation <NUM>, the target cell (e.g., <NUM>) 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 <NUM> 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 <NUM>, the source cell <NUM> communicates a conditional handover command (e.g., the conditional handover command received from the first target cell <NUM> with the handover acknowledgment at operation <NUM> is forwarded) together with the high threshold to the UE <NUM>.

Once the UE receives the conditional HO command at operation <NUM>, the UE maintains a connection with the source/serving cell <NUM>. 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 <NUM>, a measurement report (for the second target cell <NUM>) 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 <NUM>, by the source cell <NUM>.

At operation <NUM>, the source cell <NUM> can make a handover decision for handover to the second target cell <NUM> based on the received measurement report at operation <NUM>.

At operation <NUM>, the source cell <NUM> communicates a handover request to the second target cell <NUM>. 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 <NUM>).

At operation <NUM>, the second target cell <NUM> accepts the handover request.

At operation <NUM>, the second target cell <NUM> communicates a handover acknowledgment to the source cell <NUM>. 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 <NUM>).

At operation <NUM>, the source cell <NUM> communicates a conditional handover command (e.g., the conditional handover command received from the second target cell <NUM> with the handover acknowledgment at operation <NUM>) together with the high threshold to the UE <NUM>.

At operation <NUM>, the UE <NUM> 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 <NUM> satisfies the high threshold communicated with the conditional handover command (e.g., at operation <NUM>).

At operation <NUM>, synchronization and random access procedure can take place between the UE <NUM> and the first target cell <NUM>. At operation <NUM>, the UE <NUM> can communicate a handover completion message to the first target cell <NUM>, such as an RRC Connection Reconfiguration Complete message.

After operation <NUM>, the target cell <NUM> sends a HO complete message to the serving cell to indicate the HO is completed. The serving cell <NUM> sends resources release message to all other configured target cells so that they can release the resources they are holding for UE <NUM>.

Observation <NUM>: 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 <NUM>: the UE considers all HO commands sent to the UE. Option <NUM>: the UE considers all HO commands sent to the UE with a timer, as long as the timer is valid. Option <NUM>: the UE considers all HO commands until the target cell exits the measurement event. Option <NUM>: the UE considers only the last HO command. Option <NUM>: 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> illustrates events for conditional handover <NUM> and legacy handover <NUM> in a timeline, in accordance with some aspects. The conditional HO <NUM> may include the following operations: the UE sends a measurement report (MR) for cell <NUM> at operation <NUM>; the UE sends an MR for cell <NUM> at operation <NUM>; the network sends an HO command (for cell <NUM>) to the UE at operation <NUM>; the network sends an HO command (for cell <NUM>) to the UE at operation <NUM>; UE sends an MR for cell <NUM> at operation <NUM>; the UE executes conditional HO to cell <NUM>.

The legacy HO <NUM> may include the following operations: upon an event trigger, the UE sends an MR to the network at operation <NUM>, the network sends a HO command to the UE at operation <NUM>, and the UE performs the HO to the target at operation <NUM>.

<FIG> shows that conditional handover triggers earlier measurement reporting by configuring a smaller offset/threshold (e.g., configure A3 offset = <NUM> dB instead of <NUM> dB). A higher threshold (e.g., <NUM> 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 <NUM>: Conditional HO tends to have a longer handover duration than legacy HO.

Table <NUM> 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 0dB to 1dB, 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 <NUM>: Conditional HO reduces HOF rate in a trade-off of air interface and X2 signaling overhead.

<FIG> 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 <NUM> 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 <NUM> 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 <NUM> follow.

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

In an example, the software may reside on a communication device-readable medium.

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) <NUM> may include a hardware processor <NUM> (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory <NUM>, a static memory <NUM>, and mass storage <NUM> (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) <NUM>.

The communication device <NUM> may further include a display device <NUM>, an alphanumeric input device <NUM> (e.g., a keyboard), and a user interface (UI) navigation device <NUM> (e.g., a mouse). In an example, the display device <NUM>, input device <NUM> and UI navigation device <NUM> may be a touchscreen display. The communication device <NUM> may additionally include a signal generation device <NUM> (e.g., a speaker), a network interface device <NUM>, and one or more sensors <NUM>, such as a global positioning system (GPS) sensor, compass, accelerometer, or another sensor. The communication device <NUM> may include an output controller <NUM>, 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 <NUM> may include a communication device-readable medium <NUM>, on which is stored one or more sets of data structures or instructions <NUM> (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 <NUM>, the main memory <NUM>, the static memory <NUM>, and/or the mass storage <NUM> may be, or include (completely or at least partially), the device-readable medium <NUM>, on which is stored the one or more sets of data structures or instructions <NUM>, 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 <NUM>, the main memory <NUM>, the static memory <NUM>, or the mass storage <NUM> may constitute the device-readable medium <NUM>.

As used herein, the term "device-readable medium" is interchangeable with "computer-readable medium" or "machine-readable medium". While the communication device-readable medium <NUM> 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 <NUM>. 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 <NUM>) for execution by the communication device <NUM> and that cause the communication device <NUM> 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 <NUM> may further be transmitted or received over a communications network <NUM> using a transmission medium via the network interface device <NUM> utilizing any one of a number of transfer protocols. In an example, the network interface device <NUM> 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 <NUM>. In an example, the network interface device <NUM> 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 <NUM> 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 <NUM>, 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.

Claim 1:
A method performed
at a user equipment, UE, device (<NUM>), in association with a conditional handover between a source base station, SBS (<NUM>), and a target base station, TBS (<NUM>), in a wireless network, the method comprising:
receiving, from the SBS (<NUM>), measurement configuration information, the measurement configuration information indicating a first threshold associated with a measurement event related to the TBS (<NUM>), 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 (<NUM>), 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 (<NUM>) to the TBS (<NUM>), the conditional handover command indicating a second threshold for the measurement event, wherein the conditional handover command is based on a handover acknowledgement from the TBS (<NUM>) responsive to a conditional handover request from the SBS (<NUM>) to the TBS (<NUM>).