WO2021036928A1

WO2021036928A1 - Conditional handover for multi-connectivity configurations

Info

Publication number: WO2021036928A1
Application number: PCT/CN2020/110476
Authority: WO
Inventors: Ozcan Ozturk; Peng Cheng; Karthika Paladugu; Gavin Bernard Horn
Original assignee: Qualcomm Incorporated
Priority date: 2019-08-23
Filing date: 2020-08-21
Publication date: 2021-03-04
Also published as: WO2021035384A1

Abstract

Methods, systems, and devices for wireless communications are described. A user equipment (UE) may initiate a conditional handover in wireless communications systems implementing dual connectivity or multi-connectivity configurations. A master node may determine a configuration for the conditional handover. The master node may communicate with secondary nodes to receive configuration information for the secondary nodes. In some examples, the master node may indicate to a set of secondary nodes that the set of secondary nodes are candidate targets for a conditional handover from the UE. The master node may indicate, to the UE, the configuration for the conditional handover, including configurations for the candidate target secondary nodes. The conditional handover configuration may also include a set of conditions or thresholds for the UE to trigger the conditional handover. If one or more of the conditions or thresholds are satisfied, the UE may then trigger the conditional handover procedure.

Description

CONDITIONAL HANDOVER FOR MULTI-CONNECTIVITY CONFIGURATIONS

CROSS-REFERENCES

The present Application for Patent claims the benefit of PCT Application No. PCT/CN2019/102175 by OZTURK et al., entitled “CONDITIONAL HANDOVER FOR MULTI-CONNECTIVITY CONFIGURATIONS, ” filed August 23, 2019, assigned to the assignee hereof.

BACKGROUND

The following relates generally to wireless communications, and more specifically to conditional handover for multi-connectivity configurations.

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include a number of base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

A UE may be configured with a master node and one or more secondary nodes in a multi-connectivity configuration. Some techniques for changing or adding secondary nodes in these configurations may be improved.

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support conditional handover for multi-connectivity configurations. Generally, the described techniques provide for handover procedures initiated by a user equipment (UE) based on conditions at the UE satisfying a threshold. Some wireless communications systems may support multi-connectivity schemes, such as dual-connectivity. In some multi-connectivity schemes, a UE may have a master node and one or more secondary nodes. In some cases, a secondary node for the UE may be changed. Techniques are described herein to support configurations and signaling for a conditional handover of a secondary node, initiated by a UE, in wireless communications systems implementing dual connectivity or multi-connectivity configurations.

A master node may determine a configuration for the conditional handover. The master node may communicate with the secondary nodes to receive configuration information for the secondary nodes. In some examples, the master node may indicate to a set of secondary nodes that the set of secondary nodes are candidate targets for a conditional handover from the UE. The master node may indicate, to the UE, the configuration for the conditional handover, including configurations for the candidate target secondary nodes. The conditional handover configuration may also include a set of conditions or thresholds for the UE to trigger the conditional handover. If one or more of the conditions or thresholds are satisfied, the UE may then trigger the conditional handover procedure.

In some examples, the UE may detect an occurrence of a trigger event and initiate a conditional handover. The UE may identify the target secondary node from a set of candidates indicated in the conditional handover configuration. To handover to the target secondary node, the UE may perform a random access procedure with the target secondary node. If the handover is successful, the UE may synchronize with the target secondary node and indicate that the conditional handover was successful to the master node. The target secondary node may also indicate the successful conditional handover to the master node, the source secondary node, or both. In some cases, the master node may release the source secondary node and request for the source secondary node to forward remaining data for the UE to the target secondary node. The source secondary node may then release the UE context and inform the master node that the UE context was released. In some examples, the UE may attempt the conditional handover, but the conditional handover may fail. The UE may inform the master node of the handover failure. When a conditional handover fails, the UE may select another candidate target secondary node to connect to, or the UE may remain connected to the source secondary node.

A method of wireless communications at a UE is described. The method may include identifying that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receiving a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identifying an occurrence of a trigger condition indicated by the conditional handover configuration, and initiating the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identify an occurrence of a trigger condition indicated by the conditional handover configuration, and initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for identifying that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receiving a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identifying an occurrence of a trigger condition indicated by the conditional handover configuration, and initiating the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identify an occurrence of a trigger condition indicated by the conditional handover configuration, and initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying a configuration for the target secondary node based on the conditional handover configuration.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, identifying the configuration for the target secondary node may include operations, features, means, or instructions for receiving, from the master node, an explicit indication of the configuration for the target secondary node.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, identifying the configuration for the target secondary node may include operations, features, means, or instructions for receiving, from the master node, an indication of a configuration for the source secondary node, and receiving a configuration delta for the target secondary node, where the configuration for the target secondary node may be determined based on the configuration for the source secondary node and the configuration delta for the target secondary node.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, identifying the configuration for the target secondary node may include operations, features, means, or instructions for receiving an indication of the configuration for the target secondary node via a Radio Resource Control (RRC) message from the master node or the source secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for successfully performing the conditional handover from the source secondary node to the target secondary node, synchronizing with the target secondary node, and dropping the source secondary node based on successfully performing the conditional handover.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for performing a random access procedure with an additional target secondary node, where the conditional handover configuration includes a secondary node addition configuration, and transmitting, to the additional target secondary node, a Radio Resource Control (RRC) message based on the secondary node addition configuration.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the RRC message may be transmitted on a signaling radio bearer configured by the master node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for attaching to the additional target secondary node based on the random access procedure, and transmitting a completion indication to the master node once the UE may have attached to the additional target secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for unsuccessfully performing the conditional handover, and transmitting an indication of the unsuccessful conditional handover to the master node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for re-attaching to the source secondary node based on the unsuccessful conditional handover.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying a candidate target secondary node based on the unsuccessful conditional handover, and attempting to attach to the candidate target secondary node based on the candidate target secondary node having a highest signal quality among a set of candidate target secondary nodes.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for re-attempting the conditional handover from the source secondary node to the target secondary node based on the target secondary node having a higher signal quality than other candidate target secondary nodes.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the indication of the unsuccessful conditional handover may be transmitted via a Radio Resource Control (RRC) message.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the indication of the unsuccessful conditional handover may be transmitted via a cell group (SCG) failure report.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for measuring a signal strength of the source secondary node, where the trigger condition may be based on the signal strength of the source secondary node satisfying a signal strength threshold.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for measuring a channel quality of a wireless communications channel used for communications with the source secondary node, where the trigger condition may be based on the channel quality of the wireless communications channel satisfying a channel quality threshold.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the target secondary node may be one of a set of candidate target secondary nodes, where the conditional handover configuration includes configuration information for each of the set of candidate target secondary nodes.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the conditional handover configuration may be received from the master node or the source secondary node.

A method of wireless communications at a base station is described. The method may include identifying that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmitting, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identifying that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

An apparatus for wireless communications at a base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to identify that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

Another apparatus for wireless communications at a base station is described. The apparatus may include means for identifying that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmitting, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identifying that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

A non-transitory computer-readable medium storing code for wireless communications at a base station is described. The code may include instructions executable by a processor to identify that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the source secondary node, a node configuration for the source secondary node, and transmitting, to the target secondary node, the node configuration for the source secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for indicating, to the target secondary node, that the conditional handover may be triggered based on the satisfaction of the trigger condition at the UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for indicating, to the UE, a configuration for the target secondary node based on the conditional handover configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting an explicit indication of the configuration for the target secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the UE, an indication of a configuration for the source secondary node, and transmitting a configuration delta for the target secondary node, where the configuration for the target secondary node may be determined based on the configuration for the source secondary node and the configuration delta for the target secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the UE, an indication that a secondary node addition procedure with an additional target secondary node may be successful, where the conditional handover configuration includes a secondary node addition procedure configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the source secondary node, an indication to release the UE based on the indication that the secondary node addition procedure may be successful.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the target secondary node, an indication that the conditional handover was successful.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the source secondary node, an indication for the source secondary node to release the UE and to forward pending data for the UE to the target secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to a set of candidate target secondary nodes, an indication that the set of candidate target secondary nodes may be released as candidates for the conditional handover for the UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the source secondary node, an indication that the source secondary node may have released UE context for the UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the UE, an indication that the conditional handover was unsuccessful.

A method of wireless communications at a base station is described. The method may include receiving an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmitting, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receiving, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

An apparatus for wireless communications at a base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

Another apparatus for wireless communications at a base station is described. The apparatus may include means for receiving an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmitting, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receiving, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

A non-transitory computer-readable medium storing code for wireless communications at a base station is described. The code may include instructions executable by a processor to receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the master node, a configuration for a source secondary node.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the master node, an indication that a conditional handover procedure for the UE from a source secondary node to the base station was successful.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the source secondary node, pending data for the UE based on the conditional handover procedure being successful and the source secondary node releasing a UE context for the UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the source secondary node over an Xn connection, an indication that the conditional handover procedure may be successful.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that a random access procedure including the random access request may be unsuccessful.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for re-attempting the random access procedure with the UE in accordance with the target secondary node configuration based on the unsuccessful random access procedure.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the master node, an indication that the UE may have attached to another candidate target secondary node based on the unsuccessful random access procedure.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the master node, an indication that the random access request for communications between the UE and the base station may be conditional based on satisfaction of a trigger condition at the UE.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the base station may be one of a set of candidate target secondary nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communications that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless communications system that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 3 illustrates an example of a process flow that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a process flow that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIGs. 5 and 6 show block diagrams of devices that support conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 7 shows a block diagram of a communications manager that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 8 shows a diagram of a system including a device that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIGs. 9 and 10 show block diagrams of devices that support conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 11 shows a block diagram of a communications manager that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIG. 12 shows a diagram of a system including a device that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

FIGs. 13 through 20 show flowcharts illustrating methods that support conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Some wireless communications systems may support multi-connectivity schemes, such as dual-connectivity. In some multi-connectivity schemes, a user equipment (UE) may have a master node and one or more secondary nodes. In some cases, a secondary node for the UE may be changed. In some wireless communications systems, a master node may determine to add or change a secondary node for a UE. The UE may report measurements for configured secondary nodes, and the master node may initiate a secondary node update if the quality of a secondary node is poor. The master node may select a target secondary node, obtain configuration information for the target secondary node, and provide the configuration information so the UE may perform a random access procedure with the target secondary node.

Handovers initiated by the master node may have some delay between the emergence of poor conditions at a source secondary node and the UE being handed over to a better, target secondary node. For example, the UE may report the measurements, but then the UE may wait for the master node to evaluate the measurements, communicate with the target secondary nodes, etc. During this time, the UE may still attempt to communicate with the secondary node as the master node makes these determinations. In some cases, the UE may even lose an RRC connection with the secondary node while the master node configures the handover procedure. Therefore, techniques are described herein to support configurations and signaling for a conditional handover in wireless communications systems implementing dual connectivity or multi-connectivity configurations. Generally, the techniques described herein enable a UE to initiate a handover from a source secondary cell to a target secondary cell based on detecting one or more conditions.

The master node may determine a configuration for the conditional handover. The master node may communicate with the secondary nodes to receive configuration information for the secondary nodes. In some cases, the configuration information for a secondary node may include an RRC configuration for that secondary node. In some examples, the master node may indicate to a set of secondary nodes that the set of secondary nodes are candidate targets for a conditional handover from the UE. The master node or a secondary node may indicate, to the UE, the configuration for the conditional handover, including configurations for the candidate target secondary nodes. The configuration for the conditional handover may also include a set of conditions or thresholds for the UE to trigger the conditional handover. If one or more of the conditions or thresholds are satisfied, the UE may then trigger the conditional handover procedure to one of the candidate target secondary nodes. Therefore, instead of a handover being initiated by the master node, the UE may initiate the conditional handover configuration based on detecting one or more of the trigger conditions.

The UE may detect an occurrence of a trigger and initiate a conditional handover. The UE may identify the target secondary node from the set candidates indicated in the conditional handover configuration. To handover to the target secondary node, the UE may perform a random access procedure with the target secondary node. If the handover is successful, the UE may synchronize with the target secondary node and indicate that the conditional handover was successful to the master node. The target secondary node may also indicate the successful conditional handover to the master node, the source secondary node, or both, for example via a backhaul link or Xn interface. In some cases, the master node may release the source secondary node and request for the source secondary node to forward remaining data for the UE to the target secondary node. The source secondary node may then release the UE context and inform the master node that the UE context was released. In some examples, the UE may attempt the conditional handover, but the conditional handover may fail. The UE may inform the master node of the handover failure. When a conditional handover fails, the UE may select another candidate target secondary node to connect to, or the UE may remain connected to the source secondary node.

Aspects of the disclosure are initially described in the context of a wireless communications system. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to conditional handover for multi-connectivity configurations.

FIG. 1 illustrates an example of a wireless communications system 100 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The wireless communications system 100 includes base stations 105, UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some cases, wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, or communications with low-cost and low-complexity devices.

Base stations 105 may wirelessly communicate with UEs 115 via one or more base station antennas. Base stations 105 described herein may include or may be referred to by those skilled in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB) , a next-generation NodeB or giga-NodeB (either of which may be referred to as a gNB) , a Home NodeB, a Home eNodeB, or some other suitable terminology. Wireless communications system 100 may include base stations 105 of different types (e.g., macro or small cell base stations) . The UEs 115 described herein may be able to communicate with various types of base stations 105 and network equipment including macro eNBs, small cell eNBs, gNBs, relay base stations, and the like.

Each base station 105 may be associated with a particular geographic coverage area 110 in which communications with various UEs 115 is supported. Each base station 105 may provide communication coverage for a respective geographic coverage area 110 via communication links 125, and communication links 125 between a base station 105 and a UE 115 may utilize one or more carriers. Communication links 125 shown in wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. Downlink transmissions may also be called forward link transmissions while uplink transmissions may also be called reverse link transmissions.

The geographic coverage area 110 for a base station 105 may be divided into sectors making up a portion of the geographic coverage area 110, and each sector may be associated with a cell. For example, each base station 105 may provide communication coverage for a macro cell, a small cell, a hot spot, or other types of cells, or various combinations thereof. In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap and overlapping geographic coverage areas 110 associated with different technologies may be supported by the same base station 105 or by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous LTE/LTE-A/LTE-A Pro or NR network in which different types of base stations 105 provide coverage for various geographic coverage areas 110.

The term “cell” refers to a logical communication entity used for communication with a base station 105 (e.g., over a carrier) , and may be associated with an identifier for distinguishing neighboring cells (e.g., a physical cell identifier (PCID) , a virtual cell identifier (VCID) ) operating via the same or a different carrier. In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., machine-type communication (MTC) , narrowband Internet-of-Things (NB-IoT) , enhanced mobile broadband (eMBB) , or others) that may provide access for different types of devices. In some cases, the term “cell” may refer to a portion of a geographic coverage area 110 (e.g., a sector) over which the logical entity operates.

UEs 115 may be dispersed throughout the wireless communications system 100, and each UE 115 may be stationary or mobile. A UE 115 may also be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client. A UE 115 may also be a personal electronic device such as a cellular phone, a personal digital assistant (PDA) , a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may also refer to a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or an MTC device, or the like, which may be implemented in various articles such as appliances, vehicles, meters, or the like.

Some UEs 115, such as MTC or IoT devices, may be low cost or low complexity devices, and may provide for automated communication between machines (e.g., via Machine-to-Machine (M2M) communication) . M2M communication or MTC may refer to data communication technologies that allow devices to communicate with one another or a base station 105 without human intervention. In some examples, M2M communication or MTC may include communications from devices that integrate sensors or meters to measure or capture information and relay that information to a central server or application program that can make use of the information or present the information to humans interacting with the program or application. Some UEs 115 may be designed to collect information or enable automated behavior of machines. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reduce power consumption, such as half-duplex communications (e.g., a mode that supports one-way communication via transmission or reception, but not transmission and reception simultaneously) . In some examples half-duplex communications may be performed at a reduced peak rate. Other power conservation techniques for UEs 115 include entering a power saving “deep sleep” mode when not engaging in active communications, or operating over a limited bandwidth (e.g., according to narrowband communications) . In some cases, UEs 115 may be designed to support critical functions (e.g., mission critical functions) , and a wireless communications system 100 may be configured to provide ultra-reliable communications for these functions.

In some cases, a UE 115 may also be able to communicate directly with other UEs 115 (e.g., using a peer-to-peer (P2P) or device-to-device (D2D) protocol) . One or more of a group of UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some cases, groups of UEs 115 communicating via D2D communications may utilize a one-to-many (1: M) system in which each UE 115 transmits to every other UE 115 in the group. In some cases, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between UEs 115 without the involvement of a base station 105.

Base stations 105 may communicate with the core network 130 and with one another. For example, base stations 105 may interface with the core network 130 through backhaul links 132 (e.g., via an S1, N2, N3, or another interface) . Base stations 105 may communicate with one another over backhaul links 134 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105) or indirectly (e.g., via core network 130) .

The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) , which may include at least one mobility management entity (MME) , at least one serving gateway (S-GW) , and at least one Packet Data Network (PDN) gateway (P-GW) . The MME may manage non-access stratum (e.g., control plane) functions such as mobility, authentication, and bearer management for UEs 115 served by base stations 105 associated with the EPC. User IP packets may be transferred through the S-GW, which itself may be connected to the P-GW. The P-GW may provide IP address allocation as well as other functions. The P-GW may be connected to the network operators IP services. The operators IP services may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched (PS) Streaming Service.

At least some of the network devices, such as a base station 105, may include subcomponents such as an access network entity, which may be an example of an access node controller (ANC) . Each access network entity may communicate with UEs 115 through a number of other access network transmission entities, which may be referred to as a radio head, a smart radio head, or a transmission/reception point (TRP) . In some configurations, various functions of each access network entity or base station 105 may be distributed across various network devices (e.g., radio heads and access network controllers) or consolidated into a single network device (e.g., a base station 105) .

Wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) . Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band, since the wavelengths range from approximately one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features. However, the waves may penetrate structures sufficiently for a macro cell to provide service to UEs 115 located indoors. Transmission of UHF waves may be associated with smaller antennas and shorter range (e.g., less than 100 km) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

Wireless communications system 100 may also operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band. The SHF region includes bands such as the 5 GHz industrial, scientific, and medical (ISM) bands, which may be used opportunistically by devices that may be capable of tolerating interference from other users.

Wireless communications system 100 may also operate in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz) , also known as the millimeter band. In some examples, wireless communications system 100 may support millimeter wave (mmW) communications between UEs 115 and base stations 105, and EHF antennas of the respective devices may be even smaller and more closely spaced than UHF antennas. In some cases, this may facilitate use of antenna arrays within a UE 115. However, the propagation of EHF transmissions may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. Techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body.

In some cases, wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, wireless communications system 100 may employ License Assisted Access (LAA) , LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz ISM band. When operating in unlicensed radio frequency spectrum bands, wireless devices such as base stations 105 and UEs 115 may employ listen-before-talk (LBT) procedures to ensure a frequency channel is clear before transmitting data. In some cases, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA) . Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination of these. Duplexing in unlicensed spectrum may be based on frequency division duplexing (FDD) , time division duplexing (TDD) , or a combination of both.

In some examples, base station 105 or UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. For example, wireless communications system 100 may use a transmission scheme between a transmitting device (e.g., a base station 105) and a receiving device (e.g., a UE 115) , where the transmitting device is equipped with multiple antennas and the receiving device is equipped with one or more antennas. MIMO communications may employ multipath signal propagation to increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers, which may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams. Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) where multiple spatial layers are transmitted to multiple devices.

Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105 or a UE 115) to shape or steer an antenna beam (e.g., a transmit beam or receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying certain amplitude and phase offsets to signals carried via each of the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation) .

In one example, a base station 105 may use multiple antennas or antenna arrays to conduct beamforming operations for directional communications with a UE 115. For instance, some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions, which may include a signal being transmitted according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by the base station 105 or a receiving device, such as a UE 115) a beam direction for subsequent transmission and/or reception by the base station 105.

Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115) . In some examples, the beam direction associated with transmissions along a single beam direction may be determined based at least in in part on a signal that was transmitted in different beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions, and the UE 115 may report to the base station 105 an indication of the signal it received with a highest signal quality, or an otherwise acceptable signal quality. Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or transmitting a signal in a single direction (e.g., for transmitting data to a receiving device) .

A receiving device (e.g., a UE 115, which may be an example of a mmW receiving device) may try multiple receive beams when receiving various signals from the base station 105, such as synchronization signals, reference signals, beam selection signals, or other control signals. For example, a receiving device may try multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets applied to signals received at a plurality of antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at a plurality of antenna elements of an antenna array, any of which may be referred to as “listening” according to different receive beams or receive directions. In some examples a receiving device may use a single receive beam to receive along a single beam direction (e.g., when receiving a data signal) . The single receive beam may be aligned in a beam direction determined based at least in part on listening according to different receive beam directions (e.g., a beam direction determined to have a highest signal strength, highest signal-to-noise ratio, or otherwise acceptable signal quality based at least in part on listening according to multiple beam directions) .

In some cases, the antennas of a base station 105 or UE 115 may be located within one or more antenna arrays, which may support MIMO operations, or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some cases, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations.

In some cases, wireless communications system 100 may be a packet-based network that operate according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use hybrid automatic repeat request (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE 115 and a base station 105 or core network 130 supporting radio bearers for user plane data. At the Physical layer, transport channels may be mapped to physical channels.

In some cases, UEs 115 and base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. HARQ feedback is one technique of increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC) ) , forward error correction (FEC) , and retransmission (e.g., automatic repeat request (ARQ) ) . HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., signal-to-noise conditions) . In some cases, a wireless device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

Time intervals in LTE or NR may be expressed in multiples of a basic time unit, which may, for example, refer to a sampling period of T _s = 1/30,720,000 seconds. Time intervals of a communications resource may be organized according to radio frames each having a duration of 10 milliseconds (ms) , where the frame period may be expressed as T _f = 307,200 T _s. The radio frames may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include 10 subframes numbered from 0 to 9, and each subframe may have a duration of 1 ms. A subframe may be further divided into 2 slots each having a duration of 0.5 ms, and each slot may contain 6 or 7 modulation symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period) . Excluding the cyclic prefix, each symbol period may contain 2048 sampling periods. In some cases, a subframe may be the smallest scheduling unit of the wireless communications system 100 and may be referred to as a transmission time interval (TTI) . In other cases, a smallest scheduling unit of the wireless communications system 100 may be shorter than a subframe or may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) or in selected component carriers using sTTIs) .

In some wireless communications systems, a slot may further be divided into multiple mini-slots containing one or more symbols. In some instances, a symbol of a mini-slot or a mini-slot may be the smallest unit of scheduling. Each symbol may vary in duration depending on the subcarrier spacing or frequency band of operation, for example. Further, some wireless communications systems may implement slot aggregation in which multiple slots or mini-slots are aggregated together and used for communication between a UE 115 and a base station 105.

The term “carrier” refers to a set of radio frequency spectrum resources having a defined physical layer structure for supporting communications over a communication link 125. For example, a carrier of a communication link 125 may include a portion of a radio frequency spectrum band that is operated according to physical layer channels for a given radio access technology. Each physical layer channel may carry user data, control information, or other signaling. A carrier may be associated with a pre-defined frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) ) and may be positioned according to a channel raster for discovery by UEs 115. Carriers may be downlink or uplink (e.g., in an FDD mode) , or be configured to carry downlink and uplink communications (e.g., in a TDD mode) . In some examples, signal waveforms transmitted over a carrier may be made up of multiple sub-carriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM) ) .

The organizational structure of the carriers may be different for different radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR) . For example, communications over a carrier may be organized according to TTIs or slots, each of which may include user data as well as control information or signaling to support decoding the user data. A carrier may also include dedicated acquisition signaling (e.g., synchronization signals or system information, etc. ) and control signaling that coordinates operation for the carrier. In some examples (e.g., in a carrier aggregation configuration) , a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers.

Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. In some examples, control information transmitted in a physical control channel may be distributed between different control regions in a cascaded manner (e.g., between a common control region or common search space and one or more UE-specific control regions or UE-specific search spaces) .

A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system 100. For example, the carrier bandwidth may be one of a number of predetermined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz) . In some examples, each served UE 115 may be configured for operating over portions or all of the carrier bandwidth. In other examples, some UEs 115 may be configured for operation using a narrowband protocol type that is associated with a predefined portion or range (e.g., set of subcarriers or RBs) within a carrier (e.g., “in-band” deployment of a narrowband protocol type) .

In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme) . Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. In MIMO systems, a wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers) , and the use of multiple spatial layers may further increase the data rate for communications with a UE 115.

Devices of the wireless communications system 100 (e.g., base stations 105 or UEs 115) may have a hardware configuration that supports communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communications system 100 may include base stations 105 and/or UEs 115 that support simultaneous communications via carriers associated with more than one different carrier bandwidth.

Wireless communications system 100 may support communication with a UE 115 on multiple cells or carriers, a feature which may be referred to as carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both FDD and TDD component carriers.

In some cases, wireless communications system 100 may utilize enhanced component carriers (eCCs) . An eCC may be characterized by one or more features including wider carrier or frequency channel bandwidth, shorter symbol duration, shorter TTI duration, or modified control channel configuration. In some cases, an eCC may be associated with a carrier aggregation configuration or a dual connectivity configuration (e.g., when multiple serving cells have a suboptimal or non-ideal backhaul link) . An eCC may also be configured for use in unlicensed spectrum or shared spectrum (e.g., where more than one operator is allowed to use the spectrum) . An eCC characterized by wide carrier bandwidth may include one or more segments that may be utilized by UEs 115 that are not capable of monitoring the whole carrier bandwidth or are otherwise configured to use a limited carrier bandwidth (e.g., to conserve power) .

In some cases, an eCC may utilize a different symbol duration than other component carriers, which may include use of a reduced symbol duration as compared with symbol durations of the other component carriers. A shorter symbol duration may be associated with increased spacing between adjacent subcarriers. A device, such as a UE 115 or base station 105, utilizing eCCs may transmit wideband signals (e.g., according to frequency channel or carrier bandwidths of 20, 40, 60, 80 MHz, etc. ) at reduced symbol durations (e.g., 16.67 microseconds) . A TTI in eCC may consist of one or multiple symbol periods. In some cases, the TTI duration (that is, the number of symbol periods in a TTI) may be variable.

Wireless communications system 100 may be an NR system that may utilize any combination of licensed, shared, and unlicensed spectrum bands, among others. The flexibility of eCC symbol duration and subcarrier spacing may allow for the use of eCC across multiple spectrums. In some examples, NR shared spectrum may increase spectrum utilization and spectral efficiency, specifically through dynamic vertical (e.g., across the frequency domain) and horizontal (e.g., across the time domain) sharing of resources.

A master base station 105 may determine a configuration for the conditional handover. The master base station 105 may communicate with secondary base stations 105 to receive configuration information for the secondary base stations 105. In some examples, the master base station 105 may indicate to a set of secondary base stations 105 that the set of secondary base stations 105 are candidate targets for a conditional handover from a UE 115. The master base station 105 or a secondary base station 105 may indicate, to the UE 115, the configuration for the conditional handover, including configurations for the candidate target secondary base stations 105. The conditional handover configuration may also include a set of conditions or thresholds for the UE to trigger the conditional handover. If one or more of the conditions or thresholds are satisfied, the UE 115 may then trigger the conditional handover procedure.

In some examples, the UE 115 may detect an occurrence of a trigger event and initiate a conditional handover. The UE 115 may identify the target secondary base station 105 from a set of candidates indicated in the conditional handover configuration. To handover to the target secondary base station 105, the UE 115 may perform a random access procedure with the target secondary base station 105. If the handover is successful, the UE may synchronize with the target secondary base station 105 and indicate that the conditional handover was successful to the master node. The target secondary base station 105 may also indicate the successful conditional handover to the master base station 105, the source secondary base station 105, or both. In some cases, the master base station 105 may release the source secondary base station 105 and request for the source secondary base station 105 to forward remaining data for the UE 115 to the target secondary base station 105. The source secondary base station 105 may then release the UE context and inform the master base station 105 that the UE context was released.

In some examples, the UE 115 may attempt the conditional handover, but the conditional handover may fail. The UE 115 may inform the master base station 105 of the handover failure. When a conditional handover fails, the UE 115 may select another candidate target secondary node to connect to, or the UE 115 may remain connected to the source secondary base station 105.

FIG. 2 illustrates an example of a wireless communications system 200 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. In some examples, wireless communications system 200 may implement aspects of wireless communications system 100. The wireless communications system 200 includes UE 115-a, which may be an example of a UE 115 as described with reference to FIG. 1. The wireless communications system 200 includes base station 105-a, base station 105-b, and base station 105-c, which may each be an example of a base station 105 as described with reference to FIG. 1.

Base station 105-a may be an example of a master node in a dual connectivity or multi-connectivity wireless communications configuration. As a master node, base station 105-a may have a direct interface with the core network. Base station 105-b and base station 105-c may each be an example of a secondary node in the dual connectivity or multi-connectivity wireless communications configuration. In some cases, base station 105-a may establish, monitor, and update some configurations for UE 115-a and the secondary nodes. UE 115-a may communicate with base station 105-a on communications link 205-a and communicate with base station 105-b on communications link 205-b.

In some cases, the wireless communications system 200 may change a secondary node for UE 115-a. In some wireless communications systems, a master node may determine to add or change a secondary node for a UE 115 based on measurements made at the UE 115, and the master node may initiate the secondary node change. For example, base station 105-a may determine to change the secondary node for UE 115-a from base station 105-b to base station 105-c. UE 115-a may generate a measurement report and provide the report to base station 105-a, the master node. Base station 105-a may then determine whether to add or change a secondary node. Base station 105-a may identify a target secondary node (e.g., base station 105-c) and obtain configuration information for the target secondary node. Base station 105-a may provide the configuration information to UE 115-a so that UE 115-a may perform a random access procedure with base station 105-c, the target secondary node. Base station 105-a may then inform the target secondary node (e.g., base station 105-c) and the source secondary node (e.g., base station 105-b) of the change.

Some wireless communications systems support a conditional handover, where a UE 115 can perform a handover to a target base station 105 based on a configuration from a source base station 105. The configuration may include conditions for when the handover should be triggered as well as a Radio Resource Control (RRC) configuration to be applied when accessing the target base station 105. Conditional handovers may be helpful to maintain a strong RRC connection at the UE 115, as the UE 115 can initiate the handover to a stronger, target base station 105 when the UE 115 detects that a connection with the source base station 105 is degrading. In some of these systems, the source base station 105 configuring the conditional handover may release the UE context once the UE 115 has been handed over to the target base station 105.

Techniques are described herein to support configurations and signaling for a conditional handover in wireless communications systems implementing dual connectivity or multi-connectivity configurations. Generally, the techniques described herein enable a UE 115 to initiate a handover from a source secondary cell to a target secondary cell based on detecting one or more conditions.

Base station 105-a may determine the configuration for the conditional handover. In some cases, the configuration for the conditional handover may include configurations for a conditional secondary node change, a conditional secondary node addition, or both. For a conditional secondary node change, UE 115-a may change the secondary node, for example from base station 105-b to base station 105-c. For a conditional secondary node addition, UE 115-a may just connect to an additional secondary node. For example, UE 115-a may perform a conditional secondary node addition to be connected to both base station 105-b and base station 105-c (e.g., at the same time) . In some cases, a UE 115-a may not always drop a node after successfully completing a conditional secondary node addition.

Base station 105-a or 105-b may communicate with the secondary nodes to receive configuration information for the secondary nodes. In some cases, the configuration information for a secondary node may include an RRC configuration for that secondary node. For example, base station 105-a may receive the latest secondary node configuration for the source secondary node, base station 105-b. Base station 105-a may communicate with the target secondary node candidates and, in some cases, signal the source secondary node configuration to the candidates. In some cases, the candidate target secondary nodes may respond to the master node with a delta configuration with respect to the source secondary node configuration. The delta configuration of a candidate target secondary node may indicate the differences between a configuration of the candidate target secondary node and the source secondary node. Indicating the delta configuration may, in some cases, reduce a signaling overhead in comparison to indicating full configurations. Additionally, or alternatively, base station 105-a may request the full configurations from the secondary nodes.

For example, base station 105-a may receive a configuration from base station 105-b. In some examples, base station 105-a may transmit the configuration for base station 105-b to base station 105-c and, in some cases, any other candidate target secondary nodes. In these examples, base station 105-a may then receive a delta configuration from base station 105-c (e.g., and any other candidate target secondary nodes) . The delta configuration may indicate any differences between the configuration of base station 105-b and base station 105-c. If base station 105-b and base station 105-c share a setting or configuration, that setting or configuration may not be included in the delta configuration (e.g., as there is no difference) . In some other examples, base station 105-a may receive indications of a full configuration from both base station 105-b, base station 105-c, and any other candidate target secondary nodes.

In some cases, base station 105-a may send a secondary node addition request to the candidate target secondary nodes with a flag indicating that the handover procedure for UE 115-a is conditional. In some cases, base station 105-a may indicate to the candidate target secondary nodes that they are candidates for a handover for UE 115-a. In some cases, the signaling between the base stations 105 may occur over an Xn interface 234.

Base station 105-a may indicate a configuration for the conditional handover to UE 115-a. In some cases, the configuration for the conditional handover may include configurations for the candidate target secondary nodes. The configuration for the conditional handover may, in some cases, also include a set of conditions or thresholds for UE 115-a to trigger the conditional handover. If one or more of the conditions or thresholds are satisfied, UE 115-a may then trigger the conditional handover procedure to one of the candidate target secondary nodes. Instead of a handover being initiated by the master node, UE 115-a may initiate the conditional handover configuration based on detecting one or more of the trigger conditions. The configuration for triggering the conditional secondary node change or the conditional secondary node addition may be indicated via an RRC message, such as for RRC reconfiguration. In some cases, base station 105-a may indicate the delta configuration for the candidate target base stations to UE 115-a, which may reduce signaling overhead for the transmission to UE 115-a (e.g., and UE 115-a may already have the RRC configuration for the source secondary node) .

Some examples of the handover trigger conditions may be based on measurements made at UE 115-a. For example, UE 115-a may measure reference signals transmitted by the source secondary station, base station 105-b. The signal strength, signal quality, or received power of the reference signals may decrease to below one or more of the thresholds indicated in the conditional handover configuration. This may trigger UE 115-a to initiate the conditional handover procedure. In some other systems, this would trigger UE 115-a to send a measurement report to base station 105-a, the master node, so that base station 105-a can initiate the handover procedure. To increase the speed of the handover (e.g., so that UE 115-a does not lose an RRC connection) , UE 115-a may instead initiate the handover procedure using the techniques described herein.

Once the conditional handover procedure is initiated, UE 115-a may identify which a target secondary node of the candidates. In some cases, the target secondary node may be identified from the candidates based on having a strong signal strength or potential connection strength. In some cases, UE 115-a may attempt to handover to the best target secondary node candidate, even if there are other, better secondary nodes.

To handover to the target secondary node, UE 115-a may perform a random access procedure with the target secondary node. In some cases, the random access procedure may be an example of a two-step random access procedure or a four-step random access procedure. UE 115-a may transmit an RRC message during or after performing the random access procedure. In some cases, the RRC message may be sent on a signaling radio bearer (SRB) which was configured by the master node and included in the conditional handover configuration.

In some cases, the conditional handover procedure may be successful, and UE 115-a may establish communications link 205-c. UE 115-a may send an indication to the master node of the secondary node addition completion. The master node (e.g., base station 105-a) may then inform the source secondary node (e.g., base station 105-b) of the handover. The master node may indicate for the source secondary node to initiate release. For example, base station 105-a may indicate for base station 105-b to release UE context for UE 115-a. In some cases, the target secondary node (e.g., base station 105-c) may inform the master node on the completion of the conditional secondary node change or conditional secondary node addition.

Once the conditional handover procedure is successfully completed, the master node may release the source secondary node. In some cases, the master node may request for the source secondary node to forward remaining data for UE 115-a to the target secondary node. For example, base station 105-a may request for base station 105-b to forward any pending data for UE 115-a to base station 105-c. The source secondary node may forward data directly to the target secondary node for terminated radio bearers. In some cases, base station 105-b may also release other candidate target secondary nodes.

In some cases, the target secondary node may inform the source secondary node on the completion of the conditional handover procedure. For example, base station 105-c may indicate that UE 115-a was successfully handed over to base station 105-c from base station 105-b. The indication may be transmitted on a backhaul link, such as Xn interface 234. In some cases, the source secondary node may release the UE context and inform the master node that the UE context was released.

In some examples, UE 115-a may attempt the conditional handover, but the conditional handover may fail. UE 115-a may inform the master node of the handover failure. In some cases, the failure may be reported via an RRC message. In some cases, the failure may be reported based on secondary cell group failure reporting. For example, the conditional handover failure may be piggybacked on a secondary cell group failure report, or the secondary cell group failure report may include a field for conditional handover failure.

When a conditional handover fails, UE 115-a may select a secondary node to connect to. In some cases, if the source secondary node is still sufficient for a connection, UE 115-a may remain connected to the source secondary node. For example, UE 115-a may autonomously fall back to the source secondary node upon failure of a conditional secondary node change if the source secondary node can still sufficiently support UE 115-a. In some cases, falling back to the source secondary node may be based on a quality of the source secondary node satisfying a threshold. In some cases, the threshold for the fallback may be different than the threshold for initiating the conditional handover procedure (e.g., and may be based on worse channel or signal conditions) .

In another example, the conditional handover may fail, and UE 115-a may attempt to another target secondary node candidate. If the current best secondary node is the target secondary node conditional handover candidate, UE 115-a may attempt to perform secondary node addition competition to that cell. For example, UE 115-a may fail a conditional secondary node change or conditional secondary node addition on base station 105-c. However, base station 105-c may still be the best (e.g., highest quality) candidate secondary node, so UE 115-a may attempt to add base station 105-c as a secondary node via a secondary node addition procedure. For example, UE 115-a may perform a random access procedure with base station 105-c. In some examples, UE 115-a may try the best target secondary node candidate, even if there are better secondary nodes. For example, one secondary node (e.g., “SN1” ) may be better quality than another secondary node (e.g., “SN2” ) , but SN2 may be configured as a candidate, and SN1 may not be configured as a candidate. Therefore, UE 115-a may attempt to connect to SN2 instead of SN1.

Using the techniques described herein, UE 115-a may initiate a handover in a multi-connectivity or dual-connectivity wireless communications system. The handover may be triggered based on a set of conditions instead of waiting for base station 105-a, the master node, to trigger the handover in response to receiving a measurement report. In some cases, the techniques for the conditional handover may be implemented alongside base station-initiated handover techniques.

FIG. 3 illustrates an example of a process flow 300 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. In some examples, the process flow 300 may implement aspects of wireless communications system 100. The process flow 300 may include UE 115-b, which may be an example of a UE 115 as described with reference to FIGs. 1 and 2. The process flow 300 may include master node 105-d, source secondary node 105-e, and target secondary node 105-f, which may be respective examples of base stations 105 may as described with reference to FIGs. 1 and 2. Master node 105-d may be an example of a master node in a dual connectivity or multi-connectivity configuration. Source secondary node 105-e and target secondary node 105-f may each be an example of a secondary node of the dual connectivity or multi-connectivity configuration.

The process flow 300 may illustrate an example of a successful conditional handover procedure initiated by UE 115-b. The master node 105-d may determine the conditional handover configuration for UE 115-b. At 305, the master node 105-d may receive RRC configurations from source secondary node 105-e and target secondary node 105-f. At 310, master node 105-d may receive, from source secondary node 105-e, a node configuration for source secondary node 105-e.

Target secondary node 105-f may receive an indication from master node 105-d that target secondary node 105-f is a candidate target secondary node for UE 115-b. In response to the indication, target secondary node 105-f may transmit a message indicative of a target secondary node configuration for communications between UE 115-b and target secondary node 105-f. In some cases, master node 105-d may transmit, to target secondary node 105-f, the node configuration for source secondary node 105-e. In some cases, target secondary node 105-f may receive the node configuration or source secondary node 105-e, and target secondary node 105-f may determine a delta configuration between the candidate target node configuration and the source node configuration. Target secondary node 105-f may transmit its node configuration, or the delta configuration, to master node 105-d.

At 315, master node 105-d or source secondary node 105-e may transmit, to UE 115-b, a conditional handover configuration which configures UE 115-b for a conditional handover from source secondary node 105-e to a candidate target secondary node (e.g., target secondary node 105-f) upon satisfaction of a trigger condition indicated in the conditional handover configuration. In some cases, the conditional handover configuration may include an explicit indication of the configuration for the target secondary node. Or, in some cases, the conditional handover configuration may include a configuration delta for target secondary node 105-f, where the configuration for target secondary node 105-f is determined based on a source secondary node configuration and the configuration delta. The conditional handover configuration may also include one or more conditions or thresholds for triggering the conditional handover.

UE 115-b may perform measurements 320 on reference signals 325 transmitted by source secondary node 105-e. For example, UE 115-b may measure a signal strength of source secondary node 105-e. Additionally, or alternatively, UE 115-b may measure a channel quality of a wireless communications channel used for communications with source secondary node 105-e. At 330, UE 115-b may identify an occurrence of a trigger condition indicated by the conditional handover configuration. For example, the signal strength of source secondary node 105-e, the channel quality of the wireless communications channel, or both, may satisfy a threshold. In an example, the signal strength of reference signals transmitted by secondary node 105-e may be measured below a threshold. UE 115-b may trigger a conditional handover based on identifying the occurrence of the trigger condition.

At 335, UE 115-b may initiate the conditional handover from source secondary node 105-e to target secondary node 105-f based on the conditional handover configuration and satisfaction of the trigger condition. In some cases, UE 115-b may identify target secondary node 105-f from a list of candidate target secondary nodes. Target secondary node 105-f may be identified based on proximity, cell loading, having a highest channel quality, or having a strongest signal strength, or any combination thereof.

For the conditional handover, UE 115-b may attempt to perform a random access procedure with target secondary node 105-f. In some cases, UE 115-b may perform a secondary node addition completion procedure to target secondary node 105-f. UE 115-b may transmit an RRC message while performing or after performing the random access procedure. In some cases, the RRC message may be transmitted to establish an RRC connection, to indicate that the handover is a conditional handover, or to indicate an RRC configuration for one or more previous nodes. In some cases, the RRC message may be an example of an RRC Connection Reconfiguration Complete message.

In the process flow 300, the conditional handover may be successful. UE 115-b may successfully perform the conditional handover from source secondary node 105-e to target secondary node 105-f and synchronize with target secondary node 105-f. In some cases, UE 115-b may drop source secondary node 105-e based on successfully performing the conditional handover. For example, if the conditional handover is a conditional secondary node change, then UE 115-b may change the secondary node from source secondary node 105-e to target secondary node 105-f, and UE 115-b may drop source secondary node 105-e. If the conditional handover is a conditional secondary node addition, then UE 115-b may just also connect to target secondary node 105-f, and UE 115-b may or may not drop, be dropped by, or be configured to drop source secondary node 105-e.

In some cases, at 340, UE 115-b may transmit a completion indication to master node 105-d once UE 115-b has attached to target secondary node 105-f. In some cases, at 345, target secondary node 105-f may inform master node 105-d and source secondary node 105-e on completion of the conditional handover.

In some examples, at 350, master node 105-d may inform source secondary node 105-e and, in some examples, initiate release of UE 115-e from source secondary node 105-e. For example, source secondary node 105-e may release UE context for UE 115-b at 355. In some cases, source secondary node 105-e may inform master node 105-d that the UE context for UE 115-b has been released. Then, UE 115-b may have switched its active secondary node from source secondary node 105-e to target secondary node 105-f.

FIG. 4 illustrates an example of a process flow 400 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. In some examples, process flow 400 may implement aspects of wireless communications system 100. The process flow 400 may include UE 115-c, which may be an example of a UE 115 as described with reference to FIGs. 1 and 2. The process flow 400 may include master node 105-g, source secondary node 105-h, and target secondary node 105-i, which may be respective examples of base stations 105 may as described with reference to FIGs. 1 and 2. Master node 105-g may be an example of a master node in a dual connectivity or multi-connectivity configuration. Source secondary node 105-h and target secondary node 105-i may each be an example of a secondary node of the dual connectivity or multi-connectivity configuration.

The process flow 400 may illustrate an example of a successful conditional handover procedure initiated by UE 115-c. The master node 105-g may determine the conditional handover configuration for UE 115-c. At 405, the master node 105-g may receive RRC configurations from source secondary node 105-h and target secondary node 105-i. At 410, master node 105-g may receive, from source secondary node 105-h, a node configuration for source secondary node 105-h.

Target secondary node 105-i may receive an indication from master node 105-g that target secondary node 105-i is a candidate target secondary node for UE 115-c. In response to the indication, target secondary node 105-i may transmit a message indicative of a target secondary node configuration for communications between UE 115-c and target secondary node 105-i. In some cases, master node 105-g may transmit, to target secondary node 105-i, the node configuration for source secondary node 105-h. In some cases, target secondary node 105-i may receive the node configuration or source secondary node 105-h, and target secondary node 105-i may determine a delta configuration between the candidate target node configuration and the source node configuration. Target secondary node 105-i may transmit its node configuration, or the delta configuration, to master node 105-g.

At 415, master node 105-g or source secondary node 105-h may transmit, to UE 115-c, a conditional handover configuration which configures UE 115-c for a conditional handover from source secondary node 105-h to a candidate target secondary node (e.g., target secondary node 105-i) upon satisfaction of a trigger condition indicated in the conditional handover configuration. In some cases, the conditional handover configuration may include an explicit indication of the configuration for the target secondary node. Or, in some cases, the conditional handover configuration may include a configuration delta for target secondary node 105-i, where the configuration for target secondary node 105-i is determined based on a source secondary node configuration and the configuration delta. The conditional handover configuration may also include one or more conditions or thresholds for triggering the conditional handover.

UE 115-c may perform measurements 420 on reference signals 425 transmitted by source secondary node 105-h. For example, UE 115-c may measure a signal strength of source secondary node 105-h. Additionally, or alternatively, UE 115-c may measure a channel quality of a wireless communications channel used for communications with source secondary node 105-h. At 430, UE 115-c may identify an occurrence of a trigger condition indicated by the conditional handover configuration. For example, the signal strength of source secondary node 105-h, the channel quality of the wireless communications channel, or both, may satisfy a threshold. In an example, the signal strength of reference signals transmitted by secondary node 105-h may be measured below a threshold. UE 115-c may trigger a conditional handover based on identifying the occurrence of the trigger condition.

At 435, UE 115-c may initiate the conditional handover from source secondary node 105-e to target secondary node 105-i based on the conditional handover configuration and satisfaction of the trigger condition. In some cases, UE 115-c may identify target secondary node 105-i from a list of candidate target secondary nodes. Target secondary node 105-i may be identified based on proximity, cell loading, having a highest channel quality, or having a strongest signal strength, or any combination thereof.

For the conditional handover, UE 115-c may attempt to perform a random access procedure with target secondary node 105-i. In some cases, UE 115-c may perform a secondary node addition completion procedure to target secondary node 105-i. UE 115-c may transmit an RRC message while performing or after performing the random access procedure. In some cases, the RRC message may be transmitted to establish an RRC connection, to indicate that the handover is a conditional handover, or to indicate an RRC configuration for one or more previous nodes. In some cases, the RRC message may be an example of an RRC Connection Reconfiguration Complete message.

In the process flow 400, the conditional handover may be unsuccessful. For example, the random access procedure may fail. At 440, UE 115-c may determine the conditional handover has failed after unsuccessfully performing the conditional handover at 435. At 445, UE 115-c may transmit an indication of the unsuccessful conditional handover to master node 105-g. In some cases, the unsuccessful conditional handover may be reported via an RRC message or based on secondary cell group failure reporting.

After the conditional handover fails, UE 115-c may either attempt to find another candidate target secondary node, or UE 115-c may fall back to source secondary node 105-h. In some cases, UE 115-c may autonomously fall back to source secondary node 105-h if source secondary node 105-h can provide a strong enough connection. For example, UE 115-c may re-attach, or remain attached, to source secondary node 105-h based on the unsuccessful conditional handover. Additionally, or alternatively, UE 115-c may attempt to connect to another target secondary node candidate.

For example, UE 115-c may identify a candidate target secondary node based on the unsuccessful conditional handover and attempt to attach to the candidate target secondary node based on the candidate target secondary node having a highest signal quality among a set of candidate target secondary nodes. In another example, UE 115-b may re-attempt the conditional handover from source secondary node 105-h to target secondary node 105-i. For example, if target secondary node 105-i has a higher signa quality than other candidate target secondary nodes, UE 115-b may re-attempt the random access procedure at 450.

FIG. 5 shows a block diagram 500 of a device 505 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 505 may be an example of aspects of a UE 115 as described herein. The device 505 may include a receiver 510, a communications manager 515, and a transmitter 520. The device 505 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 510 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to conditional handover for multi-connectivity configurations, etc. ) . Information may be passed on to other components of the device 505. The receiver 510 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The receiver 510 may utilize a single antenna or a set of antennas.

The communications manager 515 may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identify an occurrence of a trigger condition indicated by the conditional handover configuration, and initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition. The communications manager 515 may be an example of aspects of the communications manager 810 described herein.

The communications manager 515, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 515, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 515, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 515, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 515, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The actions performed by the communications manager 515 as described herein may be implemented to realize one or more potential advantages. One implementation may allow a UE 115 to trigger a handover sooner than conventional techniques. For example, if the UE 115 detects that a secondary node is degrading in quality (e.g., such that the signal strength, quality, or channel quality of the secondary node satisfies a threshold) , the UE 115 may trigger the handover. By implementing these techniques, the UE 115 may not wait for a master node to trigger a handover.

The transmitter 520 may transmit signals generated by other components of the device 505. In some examples, the transmitter 520 may be collocated with a receiver 510 in a transceiver module. For example, the transmitter 520 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The transmitter 520 may utilize a single antenna or a set of antennas.

FIG. 6 shows a block diagram 600 of a device 605 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 605 may be an example of aspects of a device 505, or a UE 115 as described herein. The device 605 may include a receiver 610, a communications manager 615, and a transmitter 640. The device 605 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 610 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to conditional handover for multi-connectivity configurations, etc. ) . Information may be passed on to other components of the device 605. The receiver 610 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The receiver 610 may utilize a single antenna or a set of antennas.

The communications manager 615 may be an example of aspects of the communications manager 515 as described herein. The communications manager 615 may include a communications configuration identifying component 620, a conditional handover configuration component 625, a trigger condition component 630, and a conditional handover initiating component 635. The communications manager 615 may be an example of aspects of the communications manager 810 described herein.

The communications configuration identifying component 620 may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node.

The conditional handover configuration component 625 may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node.

The trigger condition component 630 may identify an occurrence of a trigger condition indicated by the conditional handover configuration.

The conditional handover initiating component 635 may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

The transmitter 640 may transmit signals generated by other components of the device 605. In some examples, the transmitter 640 may be collocated with a receiver 610 in a transceiver module. For example, the transmitter 640 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The transmitter 640 may utilize a single antenna or a set of antennas.

FIG. 7 shows a block diagram 700 of a communications manager 705 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The communications manager 705 may be an example of aspects of a communications manager 515, a communications manager 615, or a communications manager 810 described herein. The communications manager 705 may include a communications configuration identifying component 710, a conditional handover configuration component 715, a trigger condition component 720, a conditional handover initiating component 725, a successful conditional handover component 730, and an unsuccessful conditional handover component 735. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The communications configuration identifying component 710 may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node.

The conditional handover configuration component 715 may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node.

In some examples, the conditional handover configuration component 715 may identify a configuration for the target secondary node based on the conditional handover configuration.

In some examples, the conditional handover configuration component 715 may receive, from the master node, an explicit indication of the configuration for the target secondary node.

In some examples, the conditional handover configuration component 715 may receive, from the master node, an indication of a configuration for the source secondary node.

In some examples, the conditional handover configuration component 715 may receive a configuration delta for the target secondary node, where the configuration for the target secondary node is determined based on the configuration for the source secondary node and the configuration delta for the target secondary node.

In some examples, the conditional handover configuration component 715 may receive an indication of the configuration for the target secondary node via a Radio Resource Control (RRC) message from the master node or the source secondary node.

In some cases, the conditional handover configuration is received from the master node or the source secondary node.

The trigger condition component 720 may identify an occurrence of a trigger condition indicated by the conditional handover configuration.

In some examples, the trigger condition component 720 may measure a signal strength of the source secondary node, where the trigger condition is based on the signal strength of the source secondary node satisfying a signal strength threshold.

In some examples, the trigger condition component 720 may measure a channel quality of a wireless communications channel used for communications with the source secondary node, where the trigger condition is based on the channel quality of the wireless communications channel satisfying a channel quality threshold.

The conditional handover initiating component 725 may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

In some cases, the target secondary node is one of a set of candidate target secondary nodes, where the conditional handover configuration includes configuration information for each of the set of candidate target secondary nodes.

The successful conditional handover component 730 may successfully perform the conditional handover from the source secondary node to the target secondary node.

In some examples, the successful conditional handover component 730 may synchronize with the target secondary node.

In some examples, the successful conditional handover component 730 may drop the source secondary node based on successfully performing the conditional handover.

In some examples, performing a random access procedure with an additional target secondary node, where the conditional handover configuration includes a secondary node addition configuration.

In some examples, the successful conditional handover component 730 may transmit, to the additional target secondary node, a Radio Resource Control (RRC) message based on the secondary node addition configuration.

In some examples, the successful conditional handover component 730 may attach to the additional target secondary node based on the random access procedure.

In some examples, the successful conditional handover component 730 may transmit a completion indication to the master node once the UE has attached to the additional target secondary node.

In some cases, the RRC message is transmitted on a signaling radio bearer configured by the master node.

The unsuccessful conditional handover component 735 may unsuccessfully perform the conditional handover.

In some examples, the unsuccessful conditional handover component 735 may transmit an indication of the unsuccessful conditional handover to the master node.

In some examples, the unsuccessful conditional handover component 735 may re-attach to the source secondary node based on the unsuccessful conditional handover.

In some examples, the unsuccessful conditional handover component 735 may identify a candidate target secondary node based on the unsuccessful conditional handover.

In some examples, the unsuccessful conditional handover component 735 may attempt to attach to the candidate target secondary node based on the candidate target secondary node having a highest signal quality among a set of candidate target secondary nodes.

In some examples, the unsuccessful conditional handover component 735 may re-attempt the conditional handover from the source secondary node to the target secondary node based on the target secondary node having a higher signal quality than other candidate target secondary nodes.

In some cases, the indication of the unsuccessful conditional handover is transmitted via a Radio Resource Control (RRC) message.

In some cases, the indication of the unsuccessful conditional handover is transmitted via a cell group (SCG) failure report.

FIG. 8 shows a diagram of a system 800 including a device 805 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 805 may be an example of or include the components of device 505, device 605, or a UE 115 as described herein. The device 805 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 810, an I/O controller 815, a transceiver 820, an antenna 825, memory 830, and a processor 840. These components may be in electronic communication via one or more buses (e.g., bus 845) .

The communications manager 810 may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node, receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node, identify an occurrence of a trigger condition indicated by the conditional handover configuration, and initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition.

The I/O controller 815 may manage input and output signals for the device 805. The I/O controller 815 may also manage peripherals not integrated into the device 805. In some cases, the I/O controller 815 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 815 may utilize an operating system such as

or another known operating system. In other cases, the I/O controller 815 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 815 may be implemented as part of a processor. In some cases, a user may interact with the device 805 via the I/O controller 815 or via hardware components controlled by the I/O controller 815.

The transceiver 820 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described herein. For example, the transceiver 820 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 820 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 825. However, in some cases the device may have more than one antenna 825, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 830 may include random-access memory (RAM) and read-only memory (ROM) . The memory 830 may store computer-readable, computer-executable code 835 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 830 may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 840 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 840 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 840. The processor 840 may be configured to execute computer- readable instructions stored in a memory (e.g., the memory 830) to cause the device 805 to perform various functions (e.g., functions or tasks supporting conditional handover for multi-connectivity configurations) .

The actions performed by the communications manager 810 as described herein may be implemented to realize one or more potential advantages at components of the device 805. For example, by initiating a conditional handoff instead of waiting for a handover procedure to be initiated by a master node, the device 805 may sooner attach to a higher quality secondary node. This may improve decoding performance for the processor 840, as the target secondary node may have improved signal strength or signal quality.

The code 835 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 835 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 835 may not be directly executable by the processor 840 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 9 shows a block diagram 900 of a device 905 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 905 may be an example of aspects of a base station 105 as described herein. The device 905 may include a receiver 910, a communications manager 915, and a transmitter 920. The device 905 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 910 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to conditional handover for multi-connectivity configurations, etc. ) . Information may be passed on to other components of the device 905. The receiver 910 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The receiver 910 may utilize a single antenna or a set of antennas.

The communications manager 915 may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration. The communications manager 915 may also receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration. The communications manager 915 may be an example of aspects of the communications manager 1210 described herein.

The communications manager 915, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 915, or its sub-components may be executed by a general-purpose processor, a DSP, an application-specific integrated circuit (ASIC) , a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 915, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 915, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 915, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 920 may transmit signals generated by other components of the device 905. In some examples, the transmitter 920 may be collocated with a receiver 910 in a transceiver module. For example, the transmitter 920 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The transmitter 920 may utilize a single antenna or a set of antennas.

FIG. 10 shows a block diagram 1000 of a device 1005 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 1005 may be an example of aspects of a device 905, or a base station 105 as described herein. The device 1005 may include a receiver 1010, a communications manager 1015, and a transmitter 1050. The device 1005 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1010 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to conditional handover for multi-connectivity configurations, etc. ) . Information may be passed on to other components of the device 1005. The receiver 1010 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The receiver 1010 may utilize a single antenna or a set of antennas.

The communications manager 1015 may be an example of aspects of the communications manager 915 as described herein. The communications manager 1015 may include a master node communications identifying component 1020, a conditional handover configuring component 1025, a conditional handover identifying component 1030, a secondary node communications identifying component 1035, a secondary node configuration component 1040, and a secondary node conditional handover component 1045. The communications manager 1015 may be an example of aspects of the communications manager 1210 described herein.

The master node communications identifying component 1020 may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE.

The conditional handover configuring component 1025 may transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration.

The conditional handover identifying component 1030 may identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

The secondary node communications identifying component 1035 may receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node.

The secondary node configuration component 1040 may transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station.

The secondary node conditional handover component 1045 may receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

The transmitter 1050 may transmit signals generated by other components of the device 1005. In some examples, the transmitter 1050 may be collocated with a receiver 1010 in a transceiver module. For example, the transmitter 1050 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The transmitter 1050 may utilize a single antenna or a set of antennas.

FIG. 11 shows a block diagram 1100 of a communications manager 1105 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The communications manager 1105 may be an example of aspects of a communications manager 915, a communications manager 1015, or a communications manager 1210 described herein. The communications manager 1105 may include a master node communications identifying component 1110, a conditional handover configuring component 1115, a conditional handover identifying component 1120, a master node successful handover component 1125, a master node unsuccessful handover component 1130, a secondary node communications identifying component 1135, a secondary node configuration component 1140, a secondary node conditional handover component 1145, a secondary node successful handover component 1150, and a secondary node unsuccessful handover component 1155. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The master node communications identifying component 1110 may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE.

The conditional handover configuring component 1115 may transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration.

In some examples, the conditional handover configuring component 1115 may receive, from the source secondary node, a node configuration for the source secondary node.

In some examples, the conditional handover configuring component 1115 may transmit, to the target secondary node, the node configuration for the source secondary node.

In some examples, the conditional handover configuring component 1115 may indicate, to the target secondary node, that the conditional handover is triggered based on the satisfaction of the trigger condition at the UE.

In some examples, the conditional handover configuring component 1115 may indicate, to the UE, a configuration for the target secondary node based on the conditional handover configuration.

In some examples, the conditional handover configuring component 1115 may transmit an explicit indication of the configuration for the target secondary node.

In some examples, the conditional handover configuring component 1115 may transmit, to the UE, an indication of a configuration for the source secondary node.

In some examples, the conditional handover configuring component 1115 may transmit a configuration delta for the target secondary node, where the configuration for the target secondary node is determined based on the configuration for the source secondary node and the configuration delta for the target secondary node.

The conditional handover identifying component 1120 may identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration.

The secondary node communications identifying component 1135 may receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node.

The secondary node configuration component 1140 may transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station.

In some examples, the secondary node configuration component 1140 may receive, from the master node, a configuration for a source secondary node.

In some examples, the secondary node configuration component 1140 may receive, from the master node, an indication that the random access request for communications between the UE and the base station is conditional based on satisfaction of a trigger condition at the UE.

In some cases, the base station is one of a set of candidate target secondary nodes.

The secondary node conditional handover component 1145 may receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

The master node successful handover component 1125 may receive, from the UE, an indication that a secondary node addition procedure with an additional target secondary node is successful, where the conditional handover configuration includes a secondary node addition procedure configuration.

In some examples, the master node successful handover component 1125 may transmit, to the source secondary node, an indication to release the UE based on the indication that the secondary node addition procedure is successful.

In some examples, the master node successful handover component 1125 may receive, from the target secondary node, an indication that the conditional handover was successful.

In some examples, the master node successful handover component 1125 may transmit, to the source secondary node, an indication for the source secondary node to release the UE and to forward pending data for the UE to the target secondary node.

In some examples, the master node successful handover component 1125 may transmit, to a set of candidate target secondary nodes, an indication that the set of candidate target secondary nodes are released as candidates for the conditional handover for the UE.

In some examples, the master node successful handover component 1125 may receive, from the source secondary node, an indication that the source secondary node has released UE context for the UE.

The master node unsuccessful handover component 1130 may receive, from the UE, an indication that the conditional handover was unsuccessful.

The secondary node successful handover component 1150 may transmit, to the master node, an indication that a conditional handover procedure for the UE from a source secondary node to the base station was successful.

In some examples, the secondary node successful handover component 1150 may receive, from the source secondary node, pending data for the UE based on the conditional handover procedure being successful and the source secondary node releasing a UE context for the UE.

In some examples, the secondary node successful handover component 1150 may transmit, to the source secondary node over an Xn connection, an indication that the conditional handover procedure is successful.

The secondary node unsuccessful handover component 1155 may determine that a random access procedure including the random access request is unsuccessful.

In some examples, the secondary node unsuccessful handover component 1155 may re-attempt the random access procedure with the UE in accordance with the target secondary node configuration based on the unsuccessful random access procedure.

In some examples, the secondary node unsuccessful handover component 1155 may receive, from the master node, an indication that the UE has attached to another candidate target secondary node based on the unsuccessful random access procedure.

FIG. 12 shows a diagram of a system 1200 including a device 1205 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The device 1205 may be an example of or include the components of device 905, device 1005, or a base station 105 as described herein. The device 1205 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1210, a network communications manager 1215, a transceiver 1220, an antenna 1225, memory 1230, a processor 1240, and an inter-station communications manager 1245. These components may be in electronic communication via one or more buses (e.g., bus 1250) .

The communications manager 1210 may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE, transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration, and identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration. The communications manager 1210 may also receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node, transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station, and receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

The network communications manager 1215 may manage communications with the core network (e.g., via one or more wired backhaul links) . For example, the network communications manager 1215 may manage the transfer of data communications for client devices, such as one or more UEs 115.

The transceiver 1220 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described herein. For example, the transceiver 1220 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1220 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1225. However, in some cases the device may have more than one antenna 1225, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1230 may include RAM, ROM, or a combination thereof. The memory 1230 may store computer-readable code 1235 including instructions that, when executed by a processor (e.g., the processor 1240) cause the device to perform various functions described herein. In some cases, the memory 1230 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1240 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1240 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1240. The processor 1240 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1230) to cause the device 1205 to perform various functions (e.g., functions or tasks supporting conditional handover for multi-connectivity configurations) .

The inter-station communications manager 1245 may manage communications with other base station 105 and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1245 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1245 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

The code 1235 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1235 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1235 may not be directly executable by the processor 1240 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 13 shows a flowchart illustrating a method 1300 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1300 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1300 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally, or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At 1305, the UE may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node. The operations of 1305 may be performed according to the methods described herein. In some examples, aspects of the operations of 1305 may be performed by a communications configuration identifying component as described with reference to FIGs. 5 through 8.

At 1310, the UE may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node. The operations of 1310 may be performed according to the methods described herein. In some examples, aspects of the operations of 1310 may be performed by a conditional handover configuration component as described with reference to FIGs. 5 through 8.

At 1315, the UE may identify an occurrence of a trigger condition indicated by the conditional handover configuration. The operations of 1315 may be performed according to the methods described herein. In some examples, aspects of the operations of 1315 may be performed by a trigger condition component as described with reference to FIGs. 5 through 8.

At 1320, the UE may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition. The operations of 1320 may be performed according to the methods described herein. In some examples, aspects of the operations of 1320 may be performed by a conditional handover initiating component as described with reference to FIGs. 5 through 8.

FIG. 14 shows a flowchart illustrating a method 1400 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1400 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1400 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally, or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At 1405, the UE may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node. The operations of 1405 may be performed according to the methods described herein. In some examples, aspects of the operations of 1405 may be performed by a communications configuration identifying component as described with reference to FIGs. 5 through 8.

At 1410, the UE may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node. The operations of 1410 may be performed according to the methods described herein. In some examples, aspects of the operations of 1410 may be performed by a conditional handover configuration component as described with reference to FIGs. 5 through 8.

At 1415, the UE may identify an occurrence of a trigger condition indicated by the conditional handover configuration. The operations of 1415 may be performed according to the methods described herein. In some examples, aspects of the operations of 1415 may be performed by a trigger condition component as described with reference to FIGs. 5 through 8.

At 1420, the UE may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition. The operations of 1420 may be performed according to the methods described herein. In some examples, aspects of the operations of 1420 may be performed by a conditional handover initiating component as described with reference to FIGs. 5 through 8.

At 1425, the UE may successfully perform the conditional handover from the source secondary node to the target secondary node. The operations of 1425 may be performed according to the methods described herein. In some examples, aspects of the operations of 1425 may be performed by a successful conditional handover component as described with reference to FIGs. 5 through 8.

At 1430, the UE may synchronize with the target secondary node. The operations of 1430 may be performed according to the methods described herein. In some examples, aspects of the operations of 1430 may be performed by a successful conditional handover component as described with reference to FIGs. 5 through 8.

At 1435, the UE may drop the source secondary node based on successfully performing the conditional handover. The operations of 1435 may be performed according to the methods described herein. In some examples, aspects of the operations of 1435 may be performed by a successful conditional handover component as described with reference to FIGs. 5 through 8.

FIG. 15 shows a flowchart illustrating a method 1500 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1500 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally, or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At 1505, the UE may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by a communications configuration identifying component as described with reference to FIGs. 5 through 8.

At 1510, the UE may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a conditional handover configuration component as described with reference to FIGs. 5 through 8.

At 1515, the UE may identify an occurrence of a trigger condition indicated by the conditional handover configuration. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a trigger condition component as described with reference to FIGs. 5 through 8.

At 1520, the UE may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a conditional handover initiating component as described with reference to FIGs. 5 through 8.

At 1525, the UE may unsuccessfully perform the conditional handover. The operations of 1525 may be performed according to the methods described herein. In some examples, aspects of the operations of 1525 may be performed by an unsuccessful conditional handover component as described with reference to FIGs. 5 through 8.

At 1530, the UE may transmit an indication of the unsuccessful conditional handover to the master node. The operations of 1530 may be performed according to the methods described herein. In some examples, aspects of the operations of 1530 may be performed by an unsuccessful conditional handover component as described with reference to FIGs. 5 through 8.

FIG. 16 shows a flowchart illustrating a method 1600 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1600 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally, or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At 1605, the UE may identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by a communications configuration identifying component as described with reference to FIGs. 5 through 8.

At 1610, the UE may receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a conditional handover configuration component as described with reference to FIGs. 5 through 8.

At 1615, the UE may identify a configuration for the target secondary node based on the conditional handover configuration. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a conditional handover configuration component as described with reference to FIGs. 5 through 8.

At 1620, the UE may identify an occurrence of a trigger condition indicated by the conditional handover configuration. The operations of 1620 may be performed according to the methods described herein. In some examples, aspects of the operations of 1620 may be performed by a trigger condition component as described with reference to FIGs. 5 through 8.

At 1625, the UE may initiate the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration and satisfaction of the trigger condition. The operations of 1625 may be performed according to the methods described herein. In some examples, aspects of the operations of 1625 may be performed by a conditional handover initiating component as described with reference to FIGs. 5 through 8.

FIG. 17 shows a flowchart illustrating a method 1700 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1700 may be performed by a communications manager as described with reference to FIGs. 9 through 12. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described herein. Additionally, or alternatively, a base station may perform aspects of the functions described herein using special-purpose hardware.

At 1705, the base station may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed by a master node communications identifying component as described with reference to FIGs. 9 through 12.

At 1710, the base station may transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed by a conditional handover configuring component as described with reference to FIGs. 9 through 12.

At 1715, the base station may identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be performed by a conditional handover identifying component as described with reference to FIGs. 9 through 12.

FIG. 18 shows a flowchart illustrating a method 1800 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1800 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1800 may be performed by a communications manager as described with reference to FIGs. 9 through 12. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described herein. Additionally, or alternatively, a base station may perform aspects of the functions described herein using special-purpose hardware.

At 1805, the base station may identify that the base station is operating as a master node in a multi-connectivity configuration for a UE. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed by a master node communications identifying component as described with reference to FIGs. 9 through 12.

At 1810, the base station may transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed by a conditional handover configuring component as described with reference to FIGs. 9 through 12.

At 1815, the base station may identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based on the conditional handover configuration. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be performed by a conditional handover identifying component as described with reference to FIGs. 9 through 12.

At 1820, the base station may receive, from the target secondary node, an indication that the conditional handover was successful. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be performed by a master node successful handover component as described with reference to FIGs. 9 through 12.

FIG. 19 shows a flowchart illustrating a method 1900 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 1900 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1900 may be performed by a communications manager as described with reference to FIGs. 9 through 12. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described herein. Additionally, or alternatively, a base station may perform aspects of the functions described herein using special-purpose hardware.

At 1905, the base station may receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node. The operations of 1905 may be performed according to the methods described herein. In some examples, aspects of the operations of 1905 may be performed by a secondary node communications identifying component as described with reference to FIGs. 9 through 12.

At 1910, the base station may transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station. The operations of 1910 may be performed according to the methods described herein. In some examples, aspects of the operations of 1910 may be performed by a secondary node configuration component as described with reference to FIGs. 9 through 12.

At 1915, the base station may receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration. The operations of 1915 may be performed according to the methods described herein. In some examples, aspects of the operations of 1915 may be performed by a secondary node conditional handover component as described with reference to FIGs. 9 through 12.

FIG. 20 shows a flowchart illustrating a method 2000 that supports conditional handover for multi-connectivity configurations in accordance with aspects of the present disclosure. The operations of method 2000 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2000 may be performed by a communications manager as described with reference to FIGs. 9 through 12. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described herein. Additionally, or alternatively, a base station may perform aspects of the functions described herein using special-purpose hardware.

At 2005, the base station may receive an indication from a master node that the base station is a candidate target secondary node for a UE operating in a multi-connectivity configuration with the master node. The operations of 2005 may be performed according to the methods described herein. In some examples, aspects of the operations of 2005 may be performed by a secondary node communications identifying component as described with reference to FIGs. 9 through 12.

At 2010, the base station may transmit, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station. The operations of 2010 may be performed according to the methods described herein. In some examples, aspects of the operations of 2010 may be performed by a secondary node configuration component as described with reference to FIGs. 9 through 12.

At 2015, the base station may receive, from the UE and based on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration. The operations of 2015 may be performed according to the methods described herein. In some examples, aspects of the operations of 2015 may be performed by a secondary node conditional handover component as described with reference to FIGs. 9 through 12.

At 2020, the base station may transmit, to the master node, an indication that a conditional handover procedure for the UE from a source secondary node to the base station was successful. The operations of 2020 may be performed according to the methods described herein. In some examples, aspects of the operations of 2020 may be performed by a secondary node successful handover component as described with reference to FIGs. 9 through 12.

It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

Example 1: A method for wireless communications at a user equipment (UE) , comprising: identifying that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node; receiving a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node; identifying an occurrence of a trigger condition indicated by the conditional handover configuration; and initiating the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration and satisfaction of the trigger condition.

Example 2: The method of example 1, further comprising: identifying a configuration for the target secondary node based at least in part on the conditional handover configuration.

Example 3: The method of any of examples 1 or 2, wherein identifying the configuration for the target secondary node comprises: receiving, from the master node, an explicit indication of the configuration for the target secondary node.

Example 4: The method of any of examples 1 to 3, wherein identifying the configuration for the target secondary node comprises: receiving, from the master node, an indication of a configuration for the source secondary node; and receiving a configuration delta for the target secondary node, wherein the configuration for the target secondary node is determined based at least in part on the configuration for the source secondary node and the configuration delta for the target secondary node.

Example 5: The method of any of examples 1 to 4, wherein identifying the configuration for the target secondary node comprises: receiving an indication of the configuration for the target secondary node via a Radio Resource Control (RRC) message from the master node or the source secondary node.

Example 6: The method of any of examples 1 to 5, further comprising: successfully performing the conditional handover from the source secondary node to the target secondary node; synchronizing with the target secondary node; and dropping the source secondary node based at least in part on successfully performing the conditional handover.

Example 7: The method of any of examples 1 to 6, further comprising: performing a random access procedure with an additional target secondary node, wherein the conditional handover configuration comprises a secondary node addition configuration; and transmitting, to the additional target secondary node, a Radio Resource Control (RRC) message based at least in part on the secondary node addition configuration.

Example 8: The method of any of examples 1 to 7, wherein the RRC message is transmitted on a signaling radio bearer configured by the master node.

Example 9: The method of any of examples 1 to 8, further comprising: attaching to the additional target secondary node based at least in part on the random access procedure; and transmitting a completion indication to the master node once the UE has attached to the additional target secondary node.

Example 10: The method of any of examples 1 to 9, further comprising: unsuccessfully performing the conditional handover; and transmitting an indication of the unsuccessful conditional handover to the master node.

Example 11: The method of any of examples 1 to 10, further comprising: re-attaching to the source secondary node based at least in part on the unsuccessful conditional handover.

Example 12: The method of any of examples 1 to 11, further comprising: identifying a candidate target secondary node based at least in part on the unsuccessful conditional handover; and attempting to attach to the candidate target secondary node based at least in part on the candidate target secondary node having a highest signal quality among a set of candidate target secondary nodes.

Example 13: The method of any of examples 1 to 12, further comprising: re-attempting the conditional handover from the source secondary node to the target secondary node based at least in part on the target secondary node having a higher signal quality than other candidate target secondary nodes.

Example 14: The method of any of examples 1 to 13, wherein the indication of the unsuccessful conditional handover is transmitted via a Radio Resource Control (RRC) message.

Example 15: The method of any of examples 1 to 13, wherein the indication of the unsuccessful conditional handover is transmitted via a cell group (SCG) failure report.

Example 16: The method of any of examples 1 to 15, further comprising: measuring a signal strength of the source secondary node, wherein the trigger condition is based at least in part on the signal strength of the source secondary node satisfying a signal strength threshold.

Example 17: The method of any of examples 1 to 16, further comprising: measuring a channel quality of a wireless communications channel used for communications with the source secondary node, wherein the trigger condition is based at least in part on the channel quality of the wireless communications channel satisfying a channel quality threshold.

Example 18: The method of any of examples 1 to 17, wherein the target secondary node is one of a plurality of candidate target secondary nodes, wherein the conditional handover configuration comprises configuration information for each of the plurality of candidate target secondary nodes.

Example 19: The method of any of examples 1 to 18, wherein the conditional handover configuration is received from the master node or the source secondary node.

Example 20: An apparatus for wireless communications comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of examples 1 to 19.

Example 21: An apparatus, comprising means for performing the method of any of examples 1 to 19.

Example 22: A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to perform a method of any of examples 1 to 19.

Example 23: A method for wireless communications at a base station, comprising: identifying that the base station is operating as a master node in a multi-connectivity configuration for a user equipment (UE) ; transmitting, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration; and identifying that the UE has initiated the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration.

Example 24: The method of example 23, further comprising: receiving, from the source secondary node, a node configuration for the source secondary node; and transmitting, to the target secondary node, the node configuration for the source secondary node.

Example 25: The method of any of examples 23 or 24, further comprising: indicating, to the target secondary node, that the conditional handover is triggered based at least in part on the satisfaction of the trigger condition at the UE.

Example 26: The method of any of examples 23 to 25, further comprising: indicating, to the UE, a configuration for the target secondary node based at least in part on the conditional handover configuration.

Example 27: The method of any of examples 23 to 26, further comprising: transmitting an explicit indication of the configuration for the target secondary node.

Example 28: The method of any of examples 23 to 27, further comprising: transmitting, to the UE, an indication of a configuration for the source secondary node; and transmitting a configuration delta for the target secondary node, wherein the configuration for the target secondary node is determined based at least in part on the configuration for the source secondary node and the configuration delta for the target secondary node.

Example 29: The method of any of examples 23 to 28, further comprising: receiving, from the UE, an indication that a secondary node addition procedure with an additional target secondary node is successful, wherein the conditional handover configuration comprises a secondary node addition procedure configuration.

Example 30: The method of any of examples 23 to 29, further comprising: transmitting, to the source secondary node, an indication to release the UE based at least in part on the indication that the secondary node addition procedure is successful.

Example 31: The method of any of examples 23 to 30, further comprising: receiving, from the target secondary node, an indication that the conditional handover was successful.

Example 32: The method of any of examples 23 to 31, further comprising: transmitting, to the source secondary node, an indication for the source secondary node to release the UE and to forward pending data for the UE to the target secondary node.

Example 33: The method of any of examples 23 to 32, further comprising: transmitting, to a set of candidate target secondary nodes, an indication that the set of candidate target secondary nodes are released as candidates for the conditional handover for the UE.

Example 34: The method of any of examples 23 to 33, further comprising: receiving, from the source secondary node, an indication that the source secondary node has released UE context for the UE.

Example 35: The method of any of examples 23 to 34, further comprising: receiving, from the UE, an indication that the conditional handover was unsuccessful.

Example 36: An apparatus for wireless communications comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of examples 23 to 35.

Example 37: An apparatus, comprising means for performing the method of any of examples 23 to 35.

Example 38: A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to perform a method of any of examples 23 to 35.

Example 39: A method for wireless communications at a base station, comprising: receiving an indication from a master node that the base station is a candidate target secondary node for a user equipment (UE) operating in a multi-connectivity configuration with the master node; transmitting, to the master node and in response to the indication, a message indicative of a target secondary node configuration for communications between the UE and the base station; and receiving, from the UE and based at least in part on the base station being a candidate target secondary node for the UE, a random access request for communications between the UE and the base station, the random access request being in accordance with the target secondary node configuration.

Example 40: The method of example 39, further comprising: receiving, from the master node, a configuration for a source secondary node.

Example 41: The method of any of examples 39 or 40, further comprising: transmitting, to the master node, an indication that a conditional handover procedure for the UE from a source secondary node to the base station was successful.

Example 42: The method of any of examples 39 to 41, further comprising: receiving, from the source secondary node, pending data for the UE based at least in part on the conditional handover procedure being successful and the source secondary node releasing a UE context for the UE.

Example 43: The method of any of examples 39 to 42, further comprising: transmitting, to the source secondary node over an Xn connection, an indication that the conditional handover procedure is successful.

Example 44: The method of any of examples 39 to 43, further comprising: determining that a random access procedure comprising the random access request is unsuccessful.

Example 45: The method of any of examples 39 to 44, further comprising: re-attempting the random access procedure with the UE in accordance with the target secondary node configuration based at least in part on the unsuccessful random access procedure.

Example 46: The method of any of examples 39 to 45, further comprising: receiving, from the master node, an indication that the UE has attached to another candidate target secondary node based at least in part on the unsuccessful random access procedure.

Example 47: The method of any of examples 39 to 46, further comprising: receiving, from the master node, an indication that the random access request for communications between the UE and the base station is conditional based at least in part on satisfaction of a trigger condition at the UE.

Example 48: The method of any of examples 39 to 47, wherein the base station is one of a plurality of candidate target secondary nodes.

Example 49: An apparatus for wireless communications comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of examples 39 to 48.

Example 50: An apparatus, comprising means for performing the method of any of examples 39 to 48.

Example 51: A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by a processor to perform a method of any of examples 39 to 48.

Techniques described herein may be used for various wireless communications systems such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , single carrier frequency division multiple access (SC-FDMA) , and other systems. A CDMA system may implement a radio technology such as CDMA2000, Universal Terrestrial Radio Access (UTRA) , etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases may be commonly referred to as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1xEV-DO, High Rate Packet Data (HRPD) , etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM) .

An OFDMA system may implement a radio technology such as Ultra Mobile Broadband (UMB) , Evolved UTRA (E-UTRA) , Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunications System (UMTS) . LTE, LTE-A, and LTE-A Pro are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR, and GSM are described in documents from the organization named “3rd Generation Partnership Project” (3GPP) . CDMA2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . The techniques described herein may be used for the systems and radio technologies mentioned herein as well as other systems and radio technologies. While aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR applications.

A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell may be associated with a lower-powered base station, as compared with a macro cell, and a small cell may operate in the same or different (e.g., licensed, unlicensed, etc. ) frequency bands as macro cells. Small cells may include pico cells, femto cells, and micro cells according to various examples. A pico cell, for example, may cover a small geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell may also cover a small geographic area (e.g., a home) and may provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells, and may also support communications using one or multiple component carriers.

The wireless communications systems described herein may support synchronous or asynchronous operation. For synchronous operation, the base stations may have similar frame timing, and transmissions from different base stations may be approximately aligned in time. For asynchronous operation, the base stations may have different frame timing, and transmissions from different base stations may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration) .

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include random-access memory (RAM) , read-only memory (ROM) , electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD) , floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an exemplary step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. ”

In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “exemplary” used herein means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

The description herein is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

A method for wireless communications at a user equipment (UE) , comprising:

identifying that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node;

receiving a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node;

identifying an occurrence of a trigger condition indicated by the conditional handover configuration; and

initiating the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration and satisfaction of the trigger condition.
The method of claim 1, further comprising:

identifying a configuration for the target secondary node based at least in part on the conditional handover configuration.
The method of claim 2, wherein identifying the configuration for the target secondary node comprises:

receiving, from the master node, an explicit indication of the configuration for the target secondary node.
The method of claim 2, wherein identifying the configuration for the target secondary node comprises:

receiving, from the master node, an indication of a configuration for the source secondary node; and

receiving a configuration delta for the target secondary node, wherein the configuration for the target secondary node is determined based at least in part on the configuration for the source secondary node and the configuration delta for the target secondary node.
The method of claim 2, wherein identifying the configuration for the target secondary node comprises:

receiving an indication of the configuration for the target secondary node via a Radio Resource Control (RRC) message from the master node or the source secondary node.
The method of claim 1, further comprising:

successfully performing the conditional handover from the source secondary node to the target secondary node;

synchronizing with the target secondary node; and

dropping the source secondary node based at least in part on successfully performing the conditional handover.
The method of claim 1, further comprising:

performing a random access procedure with an additional target secondary node, wherein the conditional handover configuration comprises a secondary node addition configuration; and

transmitting, to the additional target secondary node, a Radio Resource Control (RRC) message based at least in part on the secondary node addition configuration.
The method of claim 7, wherein the RRC message is transmitted on a signaling radio bearer configured by the master node.
The method of claim 7, further comprising:

attaching to the additional target secondary node based at least in part on the random access procedure; and

transmitting a completion indication to the master node once the UE has attached to the additional target secondary node.
The method of claim 1, further comprising:

unsuccessfully performing the conditional handover; and

transmitting an indication of the unsuccessful conditional handover to the master node.
The method of claim 10, further comprising:

re-attaching to the source secondary node based at least in part on the unsuccessful conditional handover.
The method of claim 10, further comprising:

identifying a candidate target secondary node based at least in part on the unsuccessful conditional handover; and

attempting to attach to the candidate target secondary node based at least in part on the candidate target secondary node having a highest signal quality among a set of candidate target secondary nodes.
The method of claim 10, further comprising:

re-attempting the conditional handover from the source secondary node to the target secondary node based at least in part on the target secondary node having a higher signal quality than other candidate target secondary nodes.
The method of claim 10, wherein the indication of the unsuccessful conditional handover is transmitted via a Radio Resource Control (RRC) message or via a cell group (SCG) failure report.
The method of claim 1, further comprising:

measuring a signal strength of the source secondary node, wherein the trigger condition is based at least in part on the signal strength of the source secondary node satisfying a signal strength threshold.
The method of claim 1, further comprising:

measuring a channel quality of a wireless communications channel used for communications with the source secondary node, wherein the trigger condition is based at least in part on the channel quality of the wireless communications channel satisfying a channel quality threshold.
The method of claim 1, wherein the target secondary node is one of a plurality of candidate target secondary nodes, wherein the conditional handover configuration comprises configuration information for each of the plurality of candidate target secondary nodes.
The method of claim 1, wherein the conditional handover configuration is received from the master node or the source secondary node.
A method for wireless communications at a base station, comprising:

identifying that the base station is operating as a master node in a multi-connectivity configuration for a user equipment (UE) ;

transmitting, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration; and

identifying that the UE has initiated the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration.
The method of claim 19, further comprising:

receiving, from the source secondary node, a node configuration for the source secondary node; and

transmitting, to the target secondary node, the node configuration for the source secondary node.
The method of claim 19, further comprising:

indicating, to the target secondary node, that the conditional handover is triggered based at least in part on the satisfaction of the trigger condition at the UE.
The method of claim 19, further comprising:

indicating, to the UE, a configuration for the target secondary node based at least in part on the conditional handover configuration.
The method of claim 22, further comprising:

transmitting, to the UE, an indication of a configuration for the source secondary node; and

transmitting a configuration delta for the target secondary node, wherein the configuration for the target secondary node is determined based at least in part on the configuration for the source secondary node and the configuration delta for the target secondary node.
The method of claim 19, further comprising:

receiving, from the UE, an indication that a secondary node addition procedure with an additional target secondary node is successful, wherein the conditional handover configuration comprises a secondary node addition procedure configuration; and

transmitting, to the source secondary node, an indication to release the UE based at least in part on the indication that the secondary node addition procedure is successful.
The method of claim 19, further comprising:

receiving, from the target secondary node, an indication that the conditional handover was successful; and

receiving, from the source secondary node, an indication that the source secondary node has released UE context for the UE.
The method of claim 25, further comprising:

transmitting, to the source secondary node, an indication for the source secondary node to release the UE and to forward pending data for the UE to the target secondary node.
The method of claim 25, further comprising:

transmitting, to a set of candidate target secondary nodes, an indication that the set of candidate target secondary nodes are released as candidates for the conditional handover for the UE.
The method of claim 19, further comprising:

receiving, from the UE, an indication that the conditional handover was unsuccessful.
An apparatus for wireless communications at a user equipment (UE) , comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

identify that the UE is operating in a multi-connectivity configuration with a master node and a source secondary node;

receive a conditional handover configuration which configures the UE for a conditional handover from the source secondary node to a target secondary node;

identify an occurrence of a trigger condition indicated by the conditional handover configuration; and

initiate the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration and satisfaction of the trigger condition.
An apparatus for wireless communications at a base station, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

identify that the base station is operating as a master node in a multi-connectivity configuration for a user equipment (UE) ;

transmit, to the UE, a conditional handover configuration which configures the UE for a conditional handover from a source secondary node to a target secondary node upon satisfaction of a trigger condition indicated in the conditional handover configuration; and

identify that the UE has initiated the conditional handover from the source secondary node to the target secondary node based at least in part on the conditional handover configuration.