Conditional switching in wireless networks

Abstract

A device of a user equipment (UE), the device comprising a processing circuit, wherein in order to configure the UE for conditional switching between a source base station (SBS) and a target base station (TBS) in a wireless network, the processing circuit is used to decode measurement configuration information from the SBS. The measurement configuration information indicates a measurement event and a first threshold associated with the measurement event for triggering a measurement report. The measurement report is encoded for transmission to the SBS, and the measurement report is triggered based on the first threshold. RRC signaling is received from the SBS. The RRC signaling includes a conditional switching command indicating a second threshold of the measurement event, the second threshold being higher than the first threshold. After detecting that the measurement event meets the second threshold, a handover from the SBS to the TBS is performed based on the conditional switching command.

Description

[0001] Priority claim

[0002] This patent application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 62 / 733,820, filed on September 20, 2018, and entitled “CONDITIONAL HANDOVER,” which is incorporated herein by reference in its entirety. Technical Field

[0003] Aspects relate to wireless communications. Some aspects relate to wireless networks, including 3GPP (3rd Generation Partnership Project) networks, 3GPP LTE (Long Term Evolution) networks, 3GPP LTE-A (LTE Advanced) networks, and fifth generation (5G) networks including 5G New Radio (NR) (or 5G-NR) networks and 5G-LTE networks. Other aspects relate to systems and methods for conditional handover in wireless networks. Background Art

[0004] Mobile communications have evolved significantly from early voice systems to today's highly complex integrated communications platforms. With the increase in different types of devices communicating with various network devices, the use of 3GPP LTE systems has increased. The penetration of mobile devices (user equipment or UE) in modern society continues to drive the demand for a variety of networked devices in many different environments. The fifth generation (5G) wireless system is about to be launched and is expected to achieve higher speeds, connectivity and availability. The next generation 5G network (or NR network) is expected to improve throughput, coverage and robustness, and reduce latency as well as operating and capital expenditures. 5G-NR networks will continue to develop based on 3GPP LTE-Advanced and additional potential new radio access technologies (RATs) to enrich people's lives through seamless wireless connectivity solutions, thereby providing fast and rich content and services. Since the current cellular network frequencies are saturated, higher frequencies such as millimeter wave (mm Wave) frequencies can benefit from their high bandwidth.

[0005] Potential LTE operation in unlicensed spectrum includes (and is not limited to) LTE operation in unlicensed spectrum via Dual Connectivity (DC) or DC-based LAA and standalone LTE systems, whereby LTE-based technologies operate only in unlicensed spectrum without having an "anchor" in licensed spectrum known as MulteFire. MulteFire combines the performance advantages of LTE technology with the simplicity of Wi-Fi-like deployments.

[0006] In future releases and 5G systems, it is expected that LTE systems will have further enhanced operations in both licensed and unlicensed spectrum. Such enhanced operations may include techniques for conditional handover in wireless networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the drawings, which are not necessarily drawn to scale, like numbers may describe similar components in different views. Like numbers with different letter suffixes may represent different instances of similar components. The accompanying drawings generally illustrate various aspects described in this document by way of example and not by way of limitation.

[0008] Figure 1A An architecture of a network according to some aspects is shown.

[0009] Figure 1B and Figure 1C A non-roaming 5G system architecture is shown according to some aspects.

[0010] Figure 2 A swim lane diagram showing switching based on some aspect's conditions.

[0011] Figure 3 A swim lane diagram illustrating conditional handover with more than one target cell according to some aspects.

[0012] Figure 4 Events for conditional handoff and traditional handoff are shown according to some aspects.

[0013] Figure 5 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), is shown according to some aspects. DETAILED DESCRIPTION

[0014] The following description and accompanying drawings sufficiently illustrate various aspects to enable those skilled in the art to practice these aspects. Other aspects may incorporate structural changes, logical changes, electrical changes, process changes, and other changes. Portions and features of some aspects may be included in or replace portions and features of other aspects. Aspects set forth in the claims encompass all available equivalents in those claims.

[0015] Figure 1AThe architecture of a network according to some aspects is shown. The network 140A is shown to include user equipment (UE) 101 and UE 102, which are shown as smart phones (e.g., handheld touch screen mobile computing devices capable of connecting to one or more cellular networks), but may also include any mobile or non-mobile computing devices, such as personal data assistants (PDAs), pagers, laptops, desktop computers, wireless phones, drones, or any other computing device including wired and / or wireless communication interfaces. UE 101 and UE 102 may be collectively referred to as UE 101 herein, and UE 101 may be used to perform one or more of the technologies disclosed herein.

[0016] Any radio links described herein (eg, as used in network 140A or any other illustrated network) may operate according to any exemplary radio communication technology and / or standard.

[0017] LTE and LTE-Advanced are wireless communication standards for high-speed data for UEs such as mobile phones. In LTE-Advanced and various wireless systems, carrier aggregation is a technique whereby multiple carrier signals operating at different frequencies can be used to carry communications for a single UE, thereby increasing the bandwidth available to a single device. In some aspects, carrier aggregation can be used when one or more component carriers operate at unlicensed frequencies.

[0018] The aspects described herein may be used in the context of any spectrum management scheme, including, for example, dedicated licensed spectrum, unlicensed spectrum, (licensed) shared spectrum (such as authorized shared access (ESA) at 2.3-2.4 GHz, 3.4-3.6 GHz, 3.6-3.8 GHz and other frequencies, and spectrum access system (SAS) at 3.55-3.7 GHz and other frequencies).

[0019] The aspects described herein may also be applied to different single carrier or OFDM families (CP-OFDM, SC-FDMA, SC-OFDM, filter bank based multi-carrier (FBMC), OF DMA, etc.) by assigning OFDM carrier data bit vectors to corresponding symbol resources, and are specifically applied to 3GPP NR (New Radio).

[0020] In some aspects, any one of UE 101 and UE 102 may include an Internet of Things (IoT) UE or a cellular IoT (CIoT) UE, which may include a network access layer designed for low-power IoT applications that utilize short-lived UE connections. In some aspects, any one of UE 101 and UE 102 may include a narrowband (NB) IoT UE (e.g., such as an enhanced NB-IoT (eNB-IoT) UE and a further enhanced (FeNB-IoT) UE). The IoT UE may utilize technologies such as machine-to-machine (M2M) or machine-type communication (MTC) to exchange data with an MTC server or device via a public land mobile network (PLMN), proximity-based services (ProSe) or device-to-device (D2D) communication, a sensor network, or an IoT network. The M2M or MTC data exchange may be a machine-initiated data exchange. The IoT network includes interconnected IoT UEs, which may include uniquely identifiable embedded computing devices (within an Internet infrastructure) that utilize short-lived connections. The IoT UE may execute background applications (e.g., keep-alive messages, status updates, etc.) to facilitate connectivity to the IoT network.

[0021] In some aspects, either of UE 101 and UE 102 may comprise an enhanced MTC (eMTC) UE or a further enhanced MTC (FeMTC) UE.

[0022] UE 101 and UE 102 may be configured to connect (e.g., be communicatively coupled) to a radio access network (RAN) 110. RAN 110 may be, for example, an evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN), a next generation RAN (NGRAN), or some other type of RAN. UE 101 and UE 102 utilize connection 103 and connection 104, respectively, each of which includes a physical communication interface or layer (discussed in further detail below); in this example, connection 103 and connection 104 are shown as air interfaces to achieve communicatively coupling, and may be consistent with a cellular communication protocol, 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 cellular PTT (POC) protocol, a universal mobile telecommunications system (UMTS) protocol, a 3GPP long term evolution (LTE) protocol, a fifth generation (5G) protocol, a new radio (NR) protocol, etc.

[0023] In one aspect, UE 101 and UE 102 may also directly exchange communication data via the ProSe interface 105. The ProSe interface 105 may alternatively be referred to as a sidelink interface comprising one or more logical channels including, but not limited to, a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), a physical sidelink discovery channel (PSDCH), and a physical sidelink broadcast channel (PSBCH).

[0024] UE 102 is shown as being configured to access access point (AP) 106 via connection 107. Connection 107 may include a local wireless connection such as, for example, a connection compliant with any IEEE 802.11 protocol, according to which AP 106 may include wireless fidelity. In this example, AP 106 is shown connected to the Internet and not to the core network of the wireless system (described in further detail below).

[0025] The RAN 110 may include one or more access nodes that enable the connection 103 and the connection 104. These access nodes (ANs) may be referred to as base stations (BSs), Node Bs, evolved Node Bs (eNBs), next generation Node Bs (gNBs), RAN nodes, etc., and may include ground sites (e.g., terrestrial access points) or satellite sites that cover a certain geographic area (e.g., a cell). In some aspects, the communication nodes 111 and 112 may be transmission / reception points (TRPs), and in the case where the communication nodes 111 and 112 are Node Bs (e.g., eNBs or gNBs), one or more TRPs may function within the communication cells of the Node Bs. The RAN 110 may include one or more RAN nodes (e.g., macro RAN nodes 111) for providing macro cells, and one or more RAN nodes (e.g., low power (LP) RAN nodes 112) for providing femto cells or pico cells (e.g., cells with smaller coverage areas, smaller user capacity, or higher bandwidth than macro cells).

[0026] Either of the RAN node 111 and the RAN node 112 may terminate the air interface protocol and may be the first point of contact for the UE 101 and the UE 102. In some aspects, either of the RAN node 111 and the RAN node 112 may perform various logical functions of 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 one example, either of the node 111 and / or the node 112 may be a new generation Node B (gNB), an evolved Node B (eNB), or another type of RAN node.

[0027] RAN 110 is shown as being communicatively coupled to a core network (CN) 120 via an S1 interface 113. In some aspects, CN 120 may be an evolved packet core (EPC) network, a next generation packet core (NPC) network, or some other type of CN (e.g., as described in reference to Figure 1B - as shown in FIG. 1I ). In this regard, the S1 interface 113 is divided into two parts: an S1-U interface 114, which carries communication data between the RAN node 111 and the RAN node 112 and the serving gateway (S-GW) 122; and an S1 mobility management entity (MME) interface 115, which is a signaling interface between the RAN node 111 and the RAN node 112 and the MME 121.

[0028] In this regard, CN 120 includes MME 121, S-GW 122, Packet Data Network (PDN) Gateway (P-GW) 123, and Home Subscriber Server (HSS) 124. MME 121 may be similar in function to the control plane of a conventional Serving General Packet Radio Service (GPRS) Support Node (SGSN). MME 121 may manage mobility aspects in access, such as gateway selection and tracking area list management. HSS 124 may include a database for network users, which includes subscription-related information for supporting network entities in handling communication sessions. Depending on the number of mobile subscribers, the capacity of the devices, the organization of the network, etc., CN 120 may include one or more HSS 124. For example, HSS 124 may provide support for routing / roaming authentication, authorization, naming / addressing resolution, location dependencies, etc.

[0029] The S-GW 122 may terminate the S1 interface 113 towards the RAN 110 and route data packets between the RAN 110 and the CN 120. In addition, the S-GW 122 may be a local mobility anchor for inter-RAN node handovers and may also provide an anchor for inter-3GPP mobility. Other responsibilities of the S-GW 122 may include lawful interception, charging, and some policy enforcement.

[0030] The P-GW 123 may terminate the SGi interface toward the PDN. The P-GW 123 may route data packets between the EPC network 120 and external networks such as a network including an application server 184 (alternatively referred to as an application function (AF)) via an Internet Protocol (IP) interface 125. The P-GW 123 may also transmit data to other external networks 131A, which may include the Internet, an IP Multimedia Subsystem (IPS) network, and other networks. Generally, the application server 184 may be an element that provides an application that uses IP bearer resources with a core network (e.g., a UMTS packet service (PS) domain, a LTE PS data service, etc.). In this regard, the P-GW 123 is shown as being communicatively coupled to the application server 184 via the IP interface 125. The application server 184 may also be configured to support one or more communication services (e.g., voice over Internet protocol (VoIP) sessions, PTT sessions, group communication sessions, social networking services, etc.) for the UE 101 and UE 102 via the CN 120.

[0031] The P-GW 123 may also be a node for policy enforcement and charging data collection. The Policy and Charging Rules Function (PCRF) 126 is a 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 the UE's Internet Protocol Connectivity Access Network (IP-CAN) session. In a roaming scenario with local traffic breakout, there may be two PCRFs associated with the UE's IP-CAN session: a domestic PCRF (H-PCRF) in the HPLMN and a visited PCRF (V-PCRF) in the Visited Public Land Mobile Network (VPLMN). The PCRF 126 may be communicatively coupled to the application server 184 via the P-GW 123.

[0032] In some aspects, the communication network 140A may be an IoT network. One of the current enablers of IoT is Narrowband IoT (NB-IoT).

[0033] The NG system architecture may include a RAN 110 and a 5G network core (5GC) 120. The NG-RAN 110 may include multiple nodes, such as gNBs and NG-eNBs. The core network 120 (e.g., a 5G core network or a 5GC) may include an access and mobility function (AMF) and / or a user plane function (UPF). The AMF and UPF may be communicatively coupled to the gNB and NG-eNB via an NG interface. More specifically, in some aspects, the gNB and NG-eNB may be connected to the AMF via an NG-C interface, and to the UPF via an NG-U interface. The gNB and NG-eNB may be coupled to each other via an Xn interface.

[0034] In some aspects, the NG system architecture may use reference points between various nodes as provided by 3GPP Technical Specification (TS) 23.501 (e.g., V15.4.0, 2018-12). In some aspects, each of the gNB and NG-eNB may be implemented as a base station, a mobile edge server, a small cell, a home eNB, etc. In some aspects, in the 5G architecture, the gNB may be a master node (MN) and the NG-eNB may be a secondary node (SN).

[0035] Figure 1B A non-roaming 5G system architecture is shown according to some aspects. Figure 1B , which shows a 5G system architecture 140B in a reference point representation. More specifically, the UE 102 can communicate with the RAN 110 and one or more other 5G core (5GC) network entities. The 5G system architecture 140B includes multiple network functions (NFs), such as an access and mobility management function (AMF) 132, a session management function (SMF) 136, a policy control function (PCF) 148, an application function (AF) 150, a user plane function (UPF) 134, a network slice selection function (NSSF) 142, an authentication server function (AUSF) 144, and a 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 a third-party recipient. The AMF 132 can be used to manage access control and mobility, and can also include a network slice selection function. The SMF 136 can be configured to set up and manage various sessions according to network policies. UPF 134 may be deployed in one or more configurations depending on the desired service type. PCF 148 may be configured to provide a policy framework using network slicing, mobility management, and roaming (similar to PCRF in 4G communication systems). UDM may be configured to store subscriber profiles and data (similar to HSS in 4G communication systems).

[0036] In some aspects, the 5G system architecture 140B includes an IP multimedia subsystem (IMS) 168B and multiple IP multimedia core network subsystem entities, such as a call session control function (CSCF). More specifically, the IMS 168B includes a CSCF, which can act as a proxy CSCF (P-CSCF) 162BE, a service CSCF (S-CSCF) 164B, an emergency CSCF (E-CSCF) ( Figure 1B166B. The P-CSCF 162B may be configured as the first contact point for the UE 102 within the IM subsystem (IMS) 168B. The S-CSCF 164B may be configured to handle session states in the network, and the E-CSCF may be configured to handle certain aspects of emergency sessions, such as routing emergency requests to the correct emergency center or PSAP. The I-CSCF 166B may be configured to act as a contact point within the operator's network for all IMS connections directed to subscribers of the network operator or roaming subscribers currently located within the service area of ​​the network operator. In some aspects, the I-CSCF 166B may be connected to another IP multimedia network 170E, such as an IMS operated by a different network operator.

[0037] In some aspects, the UDMZHSS 146 may be coupled to an application server 160E, which may include a telephony application server (TAS) or another application server (AS). The AS 160B may be coupled to the IMS 168B via the S-CSCF 164B or the I-CSCF 166B.

[0038] Reference point representation shows that there may be interactions between corresponding NF services. For example, Figure 1B The following reference points are shown: N1 (between UE 102 and AMF 132), N2 (between RAN 110 and AMF 132), N3 (between RAN 110 and UPF 134), N4 (between SMF 136 and UPF 134), N5 (between PCF 148 and AF 150, not shown), N6 (between UPF 134 and DN 152), N7 (between SMF 136 and PCF 148, not shown), N8 (between UDM 146 and AMF 132, not shown), N9 (between two UPFs 134, not shown), N10 (between UDM 146 and SMF 136, not shown), N11 (between AMF 132 and SMF 136, not shown), N12 (between AUSF 144 and AMF 132, not shown), N13 (between AUSF 144 and UDM 146, not shown), N14 (between two AMFs 132, not shown), N15 (between PCF 148 and AMF 132 if it is a non-roaming scenario; between PCF 148 and visited network and AMF 132 if it is 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. 1E may also be used.

[0039] Figure 1CA 5G system architecture 140C and a service-based representation are shown. Figure 1B In addition to the network entities shown in , the system architecture 140C may also include a network open function (NEF) 154 and a network repository function (NRF) 156. In some aspects, the 5G system architecture may be service-based, and the interactions between network functions may be represented by corresponding point-to-point reference points Ni or as service-based interfaces.

[0040] In some aspects, such as Figure 1C As shown, a service-based representation may be used to represent network functions within a control plane that enables other authorized network functions to access its services. In this regard, the 5G system architecture 140C may include the following service-based interfaces: Namf 158H (a service-based interface shown by AMF 132), Nsmf 1581 (a service-based interface shown by SMF 136), Nnef 158B (a service-based interface shown by NEF 154), Npcf 158D (a service-based interface shown by PCF 148), Nudm 158E (a service-based interface shown by UDM 146), Naf 158F (a service-based interface shown by AF 150), Nnrf 158C (a service-based interface shown by NRF 156), Nnssf 158A (a service-based interface shown by NSSF 142), and Nausf 158G (a service-based interface shown by AUSF 144). Figure 1C Other service-based interfaces not shown (e.g., Nudr, N5g-eir, and Nudsf).

[0041] The techniques disclosed herein may be used to reduce user data interruption during handover (HO), with a goal of being as close to 0 ms as possible (ie, the requirement may be considered relaxed), and to improve robustness during handover.

[0042] Figure 2 A swimlane diagram 200 is shown that switches conditionally according to some aspect. Figure 2 The signaling flow for a basic conditional handover between UE 202, source cell 204 and target cell 206 is shown. The key idea is to configure a "lower" threshold for one or more measurement events to trigger early measurement reporting to the serving cell. The serving cell 204 will then prepare the target cell and forward the handover command to the UE with a "higher" threshold of measurement events to improve the reliability of the handover command. When the "higher" threshold condition is met, the UE will trigger a handover (synchronization and random access procedures with the target cell) to the target cell 206. One of the problems associated with handover failure (HOF) is the failure to deliver the HO command. In a conditional handover (e.g., Figure 2As shown in FIG. 4 , the measurement report is triggered based on a lower threshold, so the HO command delivery will be more reliable.

[0043] refer to Figure 2 , at operation 208, a measurement report is triggered based on a lower threshold of a measurement event. The measurement event and the associated lower threshold may be configured by the source cell 204 before operation 208. At operation 210, the source cell 204 may make a handover decision based on the received measurement report. At operation 212, the source cell 204 transmits a handover request to the target cell 206. The handover request may include a request for conditional handover based on a higher threshold (i.e., a threshold higher than the lower threshold configured for measurement reporting in operation 208). At operation 214, the target cell 206 accepts the handover request. At operation 216, the target cell 206 transmits a handover confirmation to the source cell 204. The handover confirmation may include a conditional handover command, which includes a high threshold of a measurement event (e.g., a measurement event for triggering a measurement report in operation 208). At operation 218, the source cell 204 transmits a conditional handover command (e.g., a conditional handover command received with the handover confirmation at operation 216) together with the high threshold to the UE 202. At operation 220, UE 202 performs measurements on target cell 206 that meets the high threshold transmitted with the conditional handover command. At operation 222, synchronization and random access procedures may occur between UE 202 and target cell 206. At operation 224, the UE may transmit a handover complete message, such as an RRC connection reconfiguration complete message.

[0044] Observation 1: Conditional handover can increase the reliability of HO command delivery through early event triggering. Figure 2 A simpler case of conditional HO is shown, where only one target cell triggers the UE to send a measurement report, and when the "higher" threshold is met, the UE eventually triggers the HO. Figure 3 Different communication environments are shown in which more than one target cell triggers the UE to send a measurement report.

[0045] Figure 3 A swim lane diagram illustrating conditional handover with more than one target cell according to some aspects. Figure 3 shows a communication sequence where multiple potential target cells are triggered by a "lower" threshold and hence measurement reports are sent by the UE. Multiple target cell preparations will be required and multiple HO commands sent to the UE. Therefore, more signaling overhead in conditional handover may be associated with multiple measurement reports, preparations and HO commands. Figure 3 Use in combination.

[0046] Figure 3A conditional handover signaling flow 300 is shown, in which multiple potential target cells (e.g., a first target cell 306 and a second target cell 308) may trigger a UE 302 to send a measurement report to a source cell 304. In a conditional handover, a "lower" threshold is configured to the UE to trigger an early measurement report. After the serving cell 304 reserves resources (e.g., prepares the target cell), a HO command is 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). Since multiple potential target cells meet the "lower" threshold, multiple HO commands may be sent to the UE. This results in multiple target cell preparations, and therefore more signaling overhead on the air interface and the X2 interface due to the transmission of multiple measurement reports, preparations, and HO commands.

[0047] See also Figure 3 , at operation 310, a measurement report (for the first target cell 306) is triggered based on the lower threshold of the measurement event. The measurement event and the associated lower threshold may be configured by the source cell 304 before operation 310. More specifically, before operation 310, the network configures the lower threshold in the measurement configuration to the UE together with the measurement event. At operation 310, when the event is triggered, i.e., one or more cells meet the lower threshold configuration, the UE sends a measurement report.

[0048] At operation 312 , the source cell 304 may make a handover decision to handover to the first target cell 306 based on the measurement report received at operation 310 .

[0049] At operation 314, the source cell 304 transmits a handover request to the first target cell 306. The handover request may include a request for conditional handover based on a higher threshold (i.e., a threshold higher than the lower threshold configured for measurement reporting in operation 310). The serving cell 304 sends an early HO request to the target cell (e.g., 306) to reserve resources for the UE. The signaling may include a conditional HO request to check whether the target cell supports conditional HO (a feature that is currently not supported in traditional HO).

[0050] At operation 316 , the first target cell 306 accepts the handover request.

[0051] At operation 318, the first target cell 306 transmits a handover confirmation to the source cell 304. The handover confirmation may include a conditional handover command including a high threshold value of a measurement event (eg, the measurement event used to trigger the measurement report in operation 310).

[0052] In some aspects, at operation 318, the target cell (e.g., 306) sends a HO confirmation (ACK) or rejection to the serving cell based on support for the conditional HO. In the case of a HO ACK, the signaling at operation 318 may include the following: a HO command including RACH resources (contention-free RACH preamble); a timer for indicating a duration for which the RACH resources may be valid; an offset for indicating when the UE may exit the conditional HO; a high threshold for performing the conditional handover; and a time to trigger (TTT) parameter for the condition, wherein a measurement must meet a high threshold for the amount of TTT time.

[0053] At operation 320 , the source cell 304 transmits a conditional handover command (eg, the conditional handover command received from the first target cell 306 at operation 318 forwarded along with the handover confirmation) to the UE 302 along with the high threshold value.

[0054] Once the UE receives the conditional HO command at operation 320, the UE maintains connection with the source / serving cell 304. If the configured target cell meets the high threshold, the UE disconnects from the serving cell and performs a RACH procedure on the target cell to complete the HO. If the timer expires in the HO command, the UE discards the HO command and the target cell releases resources. If the exit condition is met, the UE sends an exit indication for the configured target cell to the serving cell.

[0055] At operation 322, a measurement report (for the second target cell 308) is triggered based on the lower threshold of the measurement event. The measurement event and the associated lower threshold may be configured by the source cell 304 prior to operation 322.

[0056] At operation 324 , the source cell 304 may make a handover decision to handover to the second target cell 306 based on the measurement report received at operation 310 .

[0057] At operation 326, the source cell 304 transmits a handover request to the second target cell 308. The handover request may include a request for conditional handover based on a higher threshold (ie, a threshold higher than the lower threshold configured for measurement reporting in operation 322).

[0058] At operation 328, the second target cell 308 accepts the handover request.

[0059] At operation 330, the second target cell 308 transmits a handover confirmation to the source cell 304. The handover confirmation may include a conditional handover command including a high threshold value of a measurement event (eg, a measurement event for triggering a measurement report in operation 322).

[0060] At operation 332 , the source cell 304 transmits a conditional handover command (eg, the conditional handover command received from the second target cell 306 along with the handover confirmation at operation 330 ) to the UE 302 along with the high threshold value.

[0061] At operation 334, the UE 302 performs measurements on one or more target cells and determines that the measurements for the first target cell 306 in the configured measurement event meet the high threshold transmitted with the conditional handover command (eg, at operation 332).

[0062] At operation 336, synchronization and random access procedures may occur between the UE 302 and the first target cell 306. At operation 338, the UE 302 may transmit a handover complete message to the first target cell 306, such as an RRC connection reconfiguration complete message.

[0063] After operation 338, the target cell 306 sends a HO complete message to the serving cell to indicate that the HO is complete. The serving cell 304 sends a resource release message to all other configured target cells so that they can release the resources they hold for the UE 302.

[0064] Observation 2: Conditional HO increases the overhead of air interface and X2 interface signaling (between cells) due to the transmission of multiple measurement reports, prepare (HO request and ACK) messages, and HO commands. In addition, conditional handover can improve the reliability of HO command delivery through early event triggering, conditional handover can be associated with a longer handover duration than traditional HO, and conditional handover can reduce the HOF rate (e.g., by providing more reliable HO command delivery) in the trade-off of increased air interface and X2 signaling overhead.

[0065] Additional aspects that may be considered in conjunction with the techniques discussed herein include whether the target cell may be configured with a contention-based RACH procedure (CBRA), which may reduce resource reservation for the UE. The following options may be used to configure such a contention-based RACH procedure.

[0066] Option 1: The target cell may only configure a contention-free RACH procedure without a timer (CFRA), which is valid until the UE handover is successful or other indications from the network.

[0067] Option 2: The target cell may configure CFRA with a timer indicating the duration for which the CFRA may be valid, after which the UE then uses CBRA.

[0068] Option 3: The target cell may be configured with CFRA with a timer; when the timer expires, the UE no longer considers the target cell and the UE will no longer fall back to CBRA.

[0069] If the timer expires, the UE can exit the conditional handover, or the UE can use contention-based RACH after the timer expires. In this case, the UE will exit the conditional handover only based on the offset (exit condition).

[0070] In some aspects, multiple HO commands may be used based on the following options.

[0071] Option 1: The UE considers all HO commands sent to the UE. Option 2: The UE considers all HO commands sent to the UE with a timer as long as the timer is valid. Option 3: The UE considers all HO commands until the target cell exits the measurement event. Option 4: The UE considers only the last HO command. Option 5: The network may indicate removal to a potential target cell for which a HO command has been sent to the UE (HO command release).

[0072] Figure 4 Events for conditional handover 400 and conventional handover 420 are shown on a timeline according to some aspects. Conditional HO 400 may include the following operations: at operation 402, the UE sends a measurement report (MR) for cell 1; at operation 404, the UE sends an MR for cell 2; at operation 406, the network sends a HO command (for cell 1) to the UE; at operation 408, the network sends a HO command (for cell 2) to the UE; at operation 410, the UE sends an MR for cell 3; the UE performs a conditional HO to cell 2.

[0073] The conventional HO 420 may include the following operations: upon event triggering, at operation 422, the UE sends a MR to the network, at operation 424, the network sends a HO command to the UE, and at operation 426, the UE performs a HO to a target.

[0074] Figure 4 It is shown that conditional handover triggers earlier measurement reporting by configuring a smaller offset / threshold (e.g., configuring A3 offset=0 dB instead of 2 dB). A higher threshold (e.g., 2 dB) can be used to trigger UE-based conditional handover. Therefore, the duration of the HO cycle in conditional HO is longer than that of conventional HO.

[0075] Observation 3: Conditional HO tends to have a longer handover duration than conventional HO.

[0076]

[0077]

[0078] Table 1: Switching performance of conditional switching compared to traditional switching

[0079] Table 1 above shows the simulation performance results of the conditional handover with different parameter settings we discussed above. The simulation results show that the handover failure (HOF) rate in conditional HO is improved due to the more reliable delivery of the HO command. However, conditional HO has more than double the signaling overhead in measurement reports and HO commands. Similarly, the X2 signaling exchange is also doubled. By increasing the trigger condition from 0dB to 1dB, the signaling overhead is reduced. This means that the signaling overhead is caused by premature triggering, but the trade-off is a slight increase in the HOF rate.

[0080] Observation 4: Conditional HO reduces the HOF rate in the trade-off between air interface and X2 signaling overhead.

[0081] Figure 5 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), is shown according to some aspects and for performing one or more of the techniques disclosed herein. In alternative aspects, the communication device 500 can operate as a standalone device or can be connected (e.g., networked) to other communication devices.

[0082] A circuit (e.g., a processing circuit) is a collection of circuits implemented in a tangible entity of the device 500, the tangible entity including hardware (e.g., simple circuits, gates, logic components, etc.). Circuit component relationships can change flexibly over time. A circuit includes components that can perform specified operations when operated (alone or in combination). In one example, the hardware of the circuit can be invariably designed to perform a specific operation (e.g., hard-wired). In one example, the hardware of the circuit can include variably connected physical components (e.g., execution units, transistors, simple circuits, etc.) to encode instructions for a specific operation, and the physical components include a machine-readable medium that is physically modified (e.g., magnetically, electrically, or removably placed invariant aggregate particles).

[0083] When the physical components are connected, the basic electrical characteristics of the hardware components change, such as from an insulator to a conductor, or vice versa. The instruction enables embedded hardware (e.g., an execution unit or a loading mechanism) to create a circuit component in hardware via a variable connection to perform certain portions of a specific operation during operation. Thus, in one example, the machine-readable medium element is part of a circuit, or is communicatively coupled to other components of the circuit when the device is operating. In one example, any of the physical components may be used in more than one component of more than one circuit. For example, during operation, an execution unit may be used in a first circuit of a first circuit system at one point in time, and reused by a second circuit in the first circuit system at a different time, or reused by a third circuit in the second circuit system. The following are additional examples of these components relative to device 500.

[0084] In some aspects, the device 500 may operate as a standalone device or may be connected (e.g., networked) to other devices. In a networked deployment, the communication device 500 may operate as a server communication device, a client communication device, or both in a server-client network environment. In one example, the communication device 500 may act as a peer communication device in a peer-to-peer (P2P) (or other distributed) network environment. The communication device 500 may be a UE, an eNB, a PC, a tablet, a STB, a PDA, a mobile phone, a smart phone, a Web device, a network router, a switch or a bridge, or any communication device capable of executing instructions (in sequence or otherwise) that specify the actions to be taken by the communication device. In addition, although only one communication device is shown, the term "communication device" should also be deemed to include any collection of communication devices that individually or collectively execute a set (or multiple sets) of instructions to perform any one or more methods discussed herein (such as cloud computing software as a service (SaaS)) and other computer cluster configurations.

[0085] Examples as described herein may include a logical component or multiple components, modules or mechanisms, or may operate on a logical component or multiple components, modules or mechanisms. A module is a tangible entity (e.g., hardware) that can perform a specified operation and may be configured or arranged in a certain manner. In one example, a circuit may be arranged as a module in a specified manner (e.g., internally or relative to an external entity such as other circuits). In one example, all or part of one or more computer systems (e.g., independent computer systems, client computer systems, or server computer systems) or one or more hardware processors may be configured by firmware or software (e.g., instructions, application parts, or applications) to operate to perform a specified operation of the module. In one example, the software may reside on a communication device readable medium. In one example, the software, when executed by the underlying hardware of the module, causes the hardware to perform a specified operation.

[0086] Thus, the term "module" should be understood to encompass a tangible entity, i.e., an entity that is physically constructed, specifically configured (e.g., hardwired), or temporarily (e.g., transiently) configured (e.g., programmed) to operate in a specified manner or to perform part or all of any operations described herein. Considering an example where a module is temporarily configured, each module need not be instantiated at any one time. For example, if a module includes a general-purpose hardware processor configured using software, the general-purpose hardware processor may be configured as corresponding different modules at different times. The software may configure the hardware processor accordingly, for example, to constitute a particular module at one instance in time and to constitute a different module at a different instance in time.

[0087] The communication device (e.g., UE) 500 may include a hardware processor 502 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 504, a static memory 506, and a mass storage device 507 (e.g., a hard drive, a tape drive, a flash memory, other block or storage devices), some or all of which may communicate with each other via an interconnection link (e.g., a bus) 508.

[0088] The communication device 500 may also include a display device 510, a mixed digital and alphanumeric input device 512 (e.g., a keyboard) and a user interface (UI) navigation device 514 (e.g., a mouse). In one example, the display device 510, the input device 512 and the UI navigation device 514 may be a touch screen display. The communication device 500 may additionally include a signal generating device 518 (e.g., a speaker), a network interface device 520, and one or more sensors 521, such as a global positioning system (GPS) sensor, a compass, an accelerometer or another sensor. The communication device 500 may include an output controller 528, such as a serial (e.g., universal serial bus (USB)) connection, a parallel connection, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection, to communicate with one or more peripheral devices (e.g., a printer, a card reader, etc.) or control the one or more peripheral devices.

[0089] The storage device 507 may include a communication device-readable medium 522 on which is stored one or more sets of data structures or instructions 524 (e.g., software) embodied or utilized by any one or more of the techniques or functionality described herein. In some aspects, the processor 502, the main memory 504, the static memory 506, and / or the registers of the mass storage 507 may (in whole or at least in part) be or include a device-readable medium 522 on which is stored one or more sets of data structures or instructions 524 embodied or utilized by any one or more of the techniques or functionality described herein. In one example, one or any combination of the hardware processor 502, the main memory 504, the static memory 506, or the mass storage 516 constitutes the device-readable medium 522.

[0090] As used herein, the term "device-readable medium" may be interchangeable with "computer-readable medium" or "machine-readable medium." Although the communication device-readable medium 522 is shown 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 one or more instructions 524. The term "communication device-readable medium" includes the terms "machine-readable medium" or "computer-readable medium" and may include any medium capable of storing, encoding, or carrying instructions (e.g., instructions 524) for execution by the communication device 500 and causing the communication device 500 to perform any one or more of the techniques of the present disclosure, or capable of storing, encoding, or carrying data structures used by or associated with such instructions. Non-limiting examples of communication device-readable media may include solid-state memory, as well as 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; 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, the communication device readable medium may include non-transitory communication device readable media. In some examples, the communication device readable medium may include communication device readable media that is not a transient propagation signal.

[0091] The instructions 524 may also be transmitted or received over the communication network 526 using any of a plurality of transmission protocols using a transmission medium via the network interface device 520. In one example, the network interface device 520 may include one or more physical jacks (e.g., Ethernet, coaxial cable, or telephone jacks) or one or more antennas to connect to the communication network 526. In one example, the network interface device 520 may include multiple antennas to communicate wirelessly using at least one of single-input multiple-output (SIMO), MIMO, or multiple-input single-output (MISO) technology. In some examples, the network interface device 520 may communicate wirelessly using multi-user MIMO technology.

[0092] The term "transmission medium" should be deemed to include any intangible medium that can store, encode or carry instructions for execution by the communication device 500, and includes a digital or analog communication signal or another intangible medium to facilitate communication of such software. In this regard, in the context of the present disclosure, a transmission medium is a device-readable medium.

[0093] Although one aspect has been described with reference to specific exemplary aspects, it will be apparent that various modifications and changes may be made to these aspects without departing from the broader scope of the present disclosure. Accordingly, the description and drawings should be regarded in an illustrative rather than a restrictive sense. Therefore, this detailed description is not to be taken in a limiting sense, and the scope of the various aspects is limited solely by the appended claims and the full scope of equivalents to which such claims are entitled.

Claims

1. An apparatus for communication, the apparatus comprising a processing circuit, wherein: In order to configure the user equipment UE for conditional handover between a source base station SBS and a target base station TBS in a wireless network, the processing circuit is configured to: decoding measurement configuration information from the SBS, the measurement configuration information indicating a measurement event and a first threshold value associated with the measurement event for triggering a measurement report; encoding a measurement report for transmission to the SBS, the measurement report being triggered based on the first threshold associated with the measurement event; decoding a radio resource control (RRC) signaling from the SBS, the RRC signaling comprising a conditional handover command, the conditional handover command being associated with a second threshold of the measurement event, the second threshold being higher than the first threshold, wherein the conditional handover command is based on a handover confirmation from the TBS, the handover confirmation being in response to a conditional handover request from the SBS to the TBS; as well as After detecting that the measurement event satisfies the second threshold, performing a handover from the SBS to the TBS based on the conditional handover command.

2. The apparatus of claim 1, wherein the conditional switch command originates from the TBS.

3. The apparatus according to claim 1, wherein the RRC signaling comprises a random access channel (RACH) resource.

4. The apparatus of claim 3, wherein the processing circuit is configured to: A RACH procedure is performed on the TBS using the RACH resource during the handover.

5. The apparatus according to claim 3, wherein the RRC signaling further comprises a timer for indicating a time period during which the RACH resource is valid.

6. The apparatus according to claim 1, wherein in response to a non-conditional handover command, the RRC connection between the UE and the SBS is terminated, and wherein in response to the conditional handover command, the RRC connection between the UE and the SBS is not terminated until the measurement event satisfies the second threshold.

7. The apparatus according to claim 1, further comprising: a transceiver circuit coupled to the processing circuit; and, one or more antennas coupled to the transceiver circuitry.

8. A non-transitory computer-readable storage medium storing instructions, wherein the instructions, when executed by one or more processors, cause a source base station SBS to perform operations to facilitate a conditional handover between the SBS and a target base station TBS in a wireless network, wherein the operations include: encoding measurement configuration information for transmission to a user equipment UE, the measurement configuration information indicating a measurement event and a first threshold value associated with the measurement event for triggering a measurement report; decoding a measurement report from the UE, the measurement report being triggered based on the first threshold associated with the measurement event; encoding a first handover request including a conditional handover request for transmission to the TBS; decoding a handover confirmation from the TBS, the handover confirmation received in response to the first handover request and including a conditional handover command for transmission to the UE; as well as Radio Resource Control (RRC) signaling is encoded for transmission to the UE, the RRC signaling including the conditional handover command for handover from the SBS to the TBS, the conditional handover command being associated with a second threshold of the measurement event, the second threshold being higher than the first threshold.

9. The non-transitory computer-readable storage medium of claim 8, wherein the handover confirmation further comprises: RACH resources for the UE to perform a random access channel RACH process, and An indication of how long the RACH resources will be available.

10. The non-transitory computer-readable storage medium of claim 8, wherein the handover confirmation further comprises: an offset for indicating when the UE can exit the handover from the SBS to the TBS; as well as The second threshold of the measurement event.

11. The non-transitory computer readable storage medium of claim 8, wherein the operations further comprise: decoding a handover completion message from the TBS, wherein the handover completion message indicates completion of the conditional handover; as well as A resource release message is encoded for transmission to at least a second target base station to release resources reserved for handover of the UE.

12. The non-transitory computer-readable storage medium of claim 8, wherein the measurement report from the UE includes measurements triggered based on the first threshold and associated with the target base station and at least a second target base station.

13. The non-transitory computer readable storage medium of claim 12, wherein the operations further comprise: encoding a second handover request for transmission to the second target base station, The handover confirmation is further received in response to the second handover request, and the handover confirmation further includes a second conditional handover command from the second target base station for transmission to the UE.

14. The non-transitory computer readable storage medium of claim 13, wherein the operations further comprise: The RRC signaling is encoded for transmission to the UE, the RRC signaling indicating a second threshold of the measurement event for handover from the SBS to the second target base station.

15. A non-transitory computer-readable storage medium storing instructions, wherein the instructions, when executed by one or more processors, cause a user equipment (UE) to perform operations to configure the UE for conditional handover between a source base station (SBS) and a target base station (TBS) in a wireless network, wherein the operations include: decoding measurement configuration information from the SBS, the measurement configuration information indicating a first threshold associated with a measurement event, wherein the first threshold is used to trigger a measurement report; encoding a measurement report for transmission to the SBS, wherein the measurement report is triggered based on the first threshold associated with the measurement event; decoding signaling from the SBS, the signaling comprising a conditional handover command, the conditional handover command being associated with a second threshold of the measurement event, the second threshold being higher than the first threshold, wherein the conditional handover command is based on a handover confirmation from the TBS, the handover confirmation being in response to a conditional handover request from the SBS to the TBS; as well as After detecting that the measurement event satisfies the second threshold, performing a handover from the SBS to the TBS based on the conditional handover command.

16. The non-transitory computer-readable storage medium of claim 15, wherein the conditional switch command originates from the TBS.

17. The non-transitory computer-readable storage medium of claim 15, wherein the signaling comprises a random access channel (RACH) resource.

18. The non-transitory computer-readable storage medium of claim 17, wherein execution of the instructions further causes the UE to: A RACH procedure is performed on the TBS using the RACH resource during the handover.

19. A method for operating a user equipment UE, comprising: decoding measurement configuration information from a source base station SBS, the measurement configuration information indicating a measurement event and a first threshold value associated with the measurement event for triggering a measurement report; encoding a measurement report for transmission to the SBS, the measurement report being triggered based on the first threshold associated with the measurement event; decoding signaling from the SBS, the signaling comprising a conditional handover command, the conditional handover command being associated with a second threshold of the measurement event, the second threshold being higher than the first threshold, wherein the conditional handover command is based on a handover confirmation from a target base station TBS, the handover confirmation being in response to a conditional handover request from the SBS to the TBS; as well as In response to a conditional handover command, a handover from the SBS to the TBS is performed after detecting that the measurement event satisfies the second threshold.

20. The method of claim 19, wherein the conditional switch command originates from the TBS.

21. The method of claim 19, wherein the signaling comprises random access channel (RACH) resources.

22. The method according to claim 21, wherein the method further comprises: A RACH procedure is performed on the TBS using the RACH resource during the handover.

23. The method according to claim 21, wherein the signaling further comprises a timer for indicating a duration for which the RACH resource is valid.

24. The method according to claim 19, in, In response to the conditional handover command, the RRC connection between the UE and the SBS is terminated until the measurement event satisfies the second threshold.

25. A method for a source base station SBS, comprising: encoding measurement configuration information for transmission to a user equipment UE, wherein the measurement configuration information indicates a first threshold associated with a measurement event, wherein the first threshold is used to trigger a measurement report; decoding a measurement report from the UE, the measurement report being triggered based on the first threshold associated with the measurement event; encoding a first handover request including a conditional handover request for transmission to a target base station TBS; decoding a handover confirmation from the TBS, the handover confirmation received in response to the first handover request and including a conditional handover command for transmission to the UE; as well as Signaling is encoded for transmission to the UE, the signaling comprising a conditional handover command for handover from the SBS to the TBS, the conditional handover command being associated with a second threshold of the measurement event, the second threshold being higher than the first threshold.

26. The method of claim 25, wherein the handover confirmation further comprises: RACH resources for the UE to perform a random access channel RACH process, and An indication of how long the RACH resources will be available.

27. The method of claim 25, wherein the handover confirmation further comprises: an offset for indicating when the UE can exit the handover from the SBS to the TBS; as well as The second threshold of the measurement event.

28. The method of claim 25, wherein the method further comprises: decoding a handover completion message from the TBS, wherein the handover completion message indicates completion of the conditional handover; as well as A resource release message is encoded for transmission to at least a second target base station to release resources reserved for handover of the UE.

29. The method of claim 25, wherein the measurement report from the UE includes measurements triggered based on the first threshold and associated with the target base station and at least a second target base station.

30. The method of claim 29, wherein the method further comprises: encoding a second handover request for transmission to the second target base station, The handover confirmation is further received in response to the second handover request, and the handover confirmation further includes a second conditional handover command from the second target base station for transmission to the UE.

31. The method of claim 30, wherein the method further comprises: The signaling is encoded for transmission to the UE, the signaling indicating a second threshold of the measurement event for handover from the SBS to the second target base station.

32. A device of a source base station SBS, the device comprising: a memory storing one or more programs; as well as One or more processors, the one or more processors being configured to execute the one or more programs stored in the memory to implement the method according to any one of claims 25 to 31.

33. A computer program product comprising program code portions for performing the method according to any one of claims 19 to 31 when the computer program product is run on one or more computing devices.

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