WO2025166558A1

WO2025166558A1 - Technologies for handover without random access

Info

Publication number: WO2025166558A1
Application number: PCT/CN2024/076411
Authority: WO
Inventors: Fangli Xu; Naveen Kumar R. PALLE VENKATA; Peng Cheng; Yuqin Chen; Ralf ROSSBACH; Ping-Heng Kuo; Alexander Sirotkin
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2024-02-06
Filing date: 2024-02-06
Publication date: 2025-08-14
Anticipated expiration: 2026-08-06

Abstract

The present application relates to devices and components, including apparatus, systems, and methods for supporting RACH-less handover.

Description

TECHNOLOGIES FOR HANDOVER WITHOUT RANDOM ACCESS

TECHNICAL FIELD

This application relates to the field of wireless networks and, in particular, to technologies for handover between cells.

BACKGROUND

Third Generation Partnership Project (3GPP) Technical Specifications (TSs) define standards for wireless networks. These TSs describe aspects related to user plane and control plane signaling over the networks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a network environment in accordance with some embodiments.

FIG. 2 illustrates timing alignment in accordance with some embodiments.

FIG. 3 illustrates a signaling diagram in accordance with some embodiments.

FIG. 4 illustrates another signaling diagram in accordance with some embodiments.

FIG. 5 illustrates another signaling diagram in accordance with some embodiments.

FIG. 6 illustrates another signaling diagram in accordance with some embodiments.

FIG. 7 illustrates another signaling diagram in accordance with some embodiments.

FIG. 8 illustrates an operation flow/algorithmic structure in accordance with some embodiments.

FIG. 9 illustrates another operation flow/algorithmic structure in accordance with some embodiments.

FIG. 10 illustrates a user equipment in accordance with some embodiments.

FIG. 11 illustrates a network node in accordance with some embodiments.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings. The same reference numbers may be used in different drawings to identify the same or similar elements. In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular structures, architectures, interfaces, and techniques in order to provide a thorough understanding of the various aspects of various embodiments. However, it will be apparent to those skilled in the art having the benefit of the present disclosure that the various aspects of the various embodiments may be practiced in other examples that depart from these specific details. In certain instances, descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the various embodiments with unnecessary detail. For the purposes of the present document, the phrases “A/B” and “A or B” mean (A) , (B) , or (A and B) ; and the phrase “based on A” means “based at least in part on A, ” for example, it could be “based solely on A” or it could be “based in part on A. ”

The following is a glossary of terms that may be used in this disclosure.

The term “circuitry” as used herein refers to, is part of, or includes hardware components that are configured to provide the described functionality. The hardware components may include an electronic circuit, a logic circuit, a processor (shared, dedicated, or group) or memory (shared, dedicated, or group) , an application specific integrated circuit (ASIC) , a field-programmable device (FPD) (e.g., a field-programmable gate array (FPGA) , a programmable logic device (PLD) , a complex PLD (CPLD) , a high-capacity PLD (HCPLD) , a structured ASIC, or a programmable system-on-a-chip (SoC) ) , or a digital signal processor (DSP) . In some embodiments, the circuitry may execute one or more software or firmware programs to provide at least some of the described functionality. The term “circuitry” may also refer to a combination of one or more hardware elements (or a combination of circuits used in an electrical or electronic system) with the program code used to carry out the functionality of that program code. In these embodiments, the combination of hardware elements and program code may be referred to as a particular type of circuitry.

The term “processor circuitry” as used herein refers to, is part of, or includes circuitry capable of sequentially and automatically carrying out a sequence of arithmetic or logical operations, or recording, storing, or transferring digital data. The term “processor circuitry” may refer an application processor, baseband processor, a central processing unit (CPU) , a graphics processing unit, a single-core processor, a dual-core processor, a triple-core processor, a quad-core processor, or any other device capable of executing or otherwise operating computer-executable instructions, such as program code, software modules, or functional processes.

The term “interface circuitry” as used herein refers to, is part of, or includes circuitry that enables the exchange of information between two or more components or devices. The term “interface circuitry” may refer to one or more hardware interfaces, for example, buses, I/O interfaces, peripheral component interfaces, and network interface cards.

The term “user equipment” or “UE” as used herein refers to a device with radio communication capabilities that may allow a user to access network resources in a communications network. The term “user equipment” or “UE” may be considered synonymous to, and may be referred to as, client, mobile, mobile device, mobile terminal, user terminal, mobile unit, mobile station, mobile user, subscriber, user, remote station, access agent, user agent, receiver, radio equipment, reconfigurable radio equipment, or reconfigurable mobile device. Furthermore, the term “user equipment” or “UE” may include any type of wireless/wired device or any computing device including a wireless communications interface.

The term “computer system” as used herein refers to any type interconnected electronic devices, computer devices, or components thereof. Additionally, the term “computer system” or “system” may refer to various components of a computer that are communicatively coupled with one another. Furthermore, the term “computer system” or “system” may refer to multiple computer devices or multiple computing systems that are communicatively coupled with one another and configured to share computing or networking resources.

The term “resource” as used herein refers to a physical or virtual device, a physical or virtual component within a computing environment, or a physical or virtual component within a particular device, such as computer devices, mechanical devices, memory space, processor/CPU time, processor/CPU usage, processor and accelerator loads, hardware time or usage, electrical power, input/output operations, ports or network sockets, channel/link allocation, throughput, memory usage, storage, network, database and applications, or workload units. A “hardware resource” may refer to compute, storage, or network resources provided by physical hardware elements. A “virtualized resource” may refer to compute, storage, or network resources provided by virtualization infrastructure to an application, device, or system. The term “network resource” or “communication resource” may refer to resources that are accessible by computer devices/systems via a communications network. The term “system resources” may refer to any kind of shared entities to provide services and may include computing or network resources. System resources may be considered as a set of coherent functions, network data objects or services, accessible through a server where such system resources reside on a single host or multiple hosts and are clearly identifiable.

The term “channel” as used herein refers to any transmission medium, either tangible or intangible, which is used to communicate data or a data stream. The term “channel” may be synonymous with or equivalent to “communications channel, ” “data communications channel, ” “transmission channel, ” “data transmission channel, ” “access channel, ” “data access channel, ” “link, ” “data link, ” “carrier, ” “radio-frequency carrier, ” or any other like term denoting a pathway or medium through which data is communicated. Additionally, the term “link” as used herein refers to a connection between two devices for the purpose of transmitting and receiving information.

The terms “instantiate, ” “instantiation, ” and the like as used herein refers to the creation of an instance. An “instance” also refers to a concrete occurrence of an object, which may occur, for example, during execution of program code.

The term “connected” may mean that two or more elements, at a common communication protocol layer, have an established signaling relationship with one another over a communication channel, link, interface, or reference point.

The term “network element” as used herein refers to physical or virtualized equipment or infrastructure used to provide wired or wireless communication network services. The term “network element” may be considered synonymous to or referred to as a networked computer, networking hardware, network equipment, network node, or a virtualized network function.

The term “information element” refers to a structural element containing one or more fields. The term “field” refers to individual contents of an information element, or a data element that contains content. An information element may include one or more additional information elements.

FIG. 1 illustrates a network environment 100 in accordance with some embodiments. In particular, the network arrangement 100 may employ one or more non-terrestrial components and may, therefore, be referred to as a non-terrestrial network (NTN) .

The network environment 100 may include user equipment (UE) 104 and a radio access network (RAN) , e.g. a network 108. The network 108 may include various network nodes such as base stations, transmit-receive points (TRPs) , etc., to facilitate the provision of one or more serving cells, e.g., serving cell 112 and target cell 114, that provide user plane and control plane protocol terminations toward the UE 104. In some embodiments, the network 108 may include a base station 102-1 to provide one or more New Radio (NR) serving cells 112. Due to mobility, the UE 104 may move out of the coverage area of the serving cell 112 and enter the coverage area of another cell, e.g., target cell 114. The network 108 may include a base station 102-2 to provide one or more target cell 114.

The network arrangement 100 may further include non-terrestrial nodes, which may also be referred to as NTN payloads (NPs) to provide transmission/reception services with respect to the UE 104. For example, the NP 110 may provide radio access services through one or more serving cells for a geographical area of the serving cell 112. The serving cell 112 provided by the NP 110 may generally correspond to a larger area than a cell associated with a terrestrial network. Coverage of one NTN cell may be across multiple jurisdictional boundaries in some embodiments.

The network arrangement 100 may further include a core network 106 coupled with the network 108. The core network 106 may provide functions and services such as authentication, network resource provisioning, and establishment, maintenance, and release of communication links. The core network 106 may provide the central infrastructure for managing and routing communication between UEs and external networks. The core network 106 may be connected to and mange one or more base stations, e.g., base stations 102-1 and 102-2.

In some embodiments, NP 110 may facilitate the provision of an access link of the serving cells. The NP 110 device may be an earth-fixed satellite (such as a geosynchronous (GEO) earth orbit satellite or a high-altitude platform station (HAPS) ) , a quasi-earth-fixed satellite (such as a non-geostationary Earth orbit (NGEO) satellite with steerable beam) , or an Earth-moving satellite (such as an NGEO with fixed or non-steerable beam) . The NP 110 may facilitate a wireless connection between the base station 102-1 and the UEs 104 by relaying signals between the two network devices. The signals may be relayed over a feeder link between the NP 110 and the base station and a service link between the NP 110 and the UE 104.

NP 100, in some embodiments, may be a network node embarked on board the satellite or high-altitude platform station, providing connectivity functions between the service link and the feeder link. If the NP 110 functions as a transparent relay, it may be referred to as a transparent NP.

The UE 104 may be connected to the serving cell 112. The serving cell 112 may include network resources configured or used to transfer information to or from the UE 104. In some conditions, the communication services provided to the UE 104 may be transferred or handed over from the serving cell 112 to another cell, e.g., the target cell 114. The transfer of the UE’s services may be referred to as a handover procedure.

In some instances, the UE 104 may move out of the coverage area of the serving cell 112 and enter the coverage area of the neighboring target cell 114. As the UE 104 moves away from the antennas, e.g., TRPs or base stations in the serving cell 112, the received signal strength from the base station may weaken, causing quality of service (QoS) degradation. At the same time, the UE 104 may get closer to transmit antennas in the target cell 114. In some instances, the NP 110 may travel and move away from the UE 104.

At some locations, the UE 104 may be able to establish a communication service with the target cell 114 that provides better quality of service, e.g., higher data rate or lower latency, than the communication service provided by the serving cell 112. Therefore, at that location, it is beneficial for the UE 104 to transfer the communications services from the serving cell 112 to the target cell 114 by initiating a handover procedure.

The handover procedure may include several steps, such as measurement and reporting, handover decision, handover execution, and handover completion. The UE 104 may periodically (or non-periodically) perform channel measurements associated with the serving cell and candidate neighboring or target cells. For example, the UE may measure the signal strength of reference signals associated with serving or target cells.

The UE 104 may send measurement reports to the network 108. The network 108 or the UE 104 may determine whether to handover to a target cell. The handover execution may be triggered by the serving cell. In one example, the network 108 may through the base station 102-1 associated with the serving cell 112 a handover command to the UE 104. In another example, the network 108 may configure the UE 104 to perform conditional handover (CHO) . The network may provide the CHO configurations and execution conditions to the UE on when and under what conditions to trigger CHO. The UE may execute the handover when one or more handover execution conditions are met. During the execution of CHO, the UE may start synchronization with the target cell and may stop monitoring the serving cell. The release of resources of the initial serving cell completes the handover procedure.

In some instances, the CHO condition may include a measurement event. For example, when a neighbor cell’s signal strength gets stronger than a threshold.

In some instances, the condition may include a time-based trigger condition. For example, CHO may be executed only during a prespecified interval, e.g., between time T1 and T2. Network 108 may configure the time-based trigger conditions, e.g., T1, T2, or the duration. The network 108 may use the information associated with the NP 110 travel schedule and location to configure the time-based trigger conditions.

In some instances, the CHO condition may include location-based trigger conditions. The CHO may be executed based on a distance between the UE 104 and a reference location. For example, the CHO may be executed when the distance between the UE 104 and a reference location is larger (or smaller) than a threshold. The UE may be configured with one or more reference locations. For example, one reference location may be associated with the serving cell, and another reference location may be associated with the target (or candidate) cell 114. The CHO may be executed when the distance between the UE 104 and a reference location associated with the serving cell 112 is larger than a threshold, and the distance between the UE 104 and a reference location associated with the target cell 114 is smaller than another threshold. The UE 104 may obtain its location using global positioning satellite (GPS) technology or other positioning technologies.

In some instances, the handover procedure may use a random access procedure using a random access channel (RACH) . Such a handover procedure may be referred to as a RACH-based handover procedure. In the RACH-based handover procedure, the UE may not be configured with uplink resources in the target cell. For example, the network may not send, in advance, an uplink grant to the UE 104 to allocate resources for uplink transmission in the target cell 114. The UE 104 may request and obtain uplink resources using a random access procedure in the target cell, e.g., by sending a random access preamble to the target cell, e.g., the base station 102-2, and exchanging random access messages as described in 3GPP TSs.

To align the uplink and downlink frames at a base station, the UEs connected to that base station may use a TA parameter to offset their transmission. The timing advance (TA) value for a given UE, e.g., the UE 104, may vary based on the UE’s mobility and its proximity to the serving base station. The UE 104 may be configured with a timer, e.g., a time alignment timer, to track the validity of the TA value.

When the UE 104 initiates a RACH-based handover execution, the UE 104 may reset the medium access control (MAC) layer (as described in 3GPP TS 38.321 v. 17.6.0 2023-09-27) . The UE 104 may not have a valid TA value and no valid uplink grant. Upon completion of the RACH procedure in the target cell 114, the UE 104 may apply a radio resource control (RRC) configuration received from the initial serving cell to the target cell 114. The UE 104 may also acquire a valid TA value and start a time alignment timer during the RACH procedure. For example, the UE may receive a valid TA value in MSG2 (message 2) associated with the random access procedure.

In some instances, the handover may be a RACH-less handover. In RACH-less handover, the network 108 may send the RACH-less handover command to the UE 104. The network 108 may include timing advance information of the target cell or a preallocated uplink grant for initial transmission in the target cell in the RACH-less handover command.

When the UE 104 receives the RACH-less handover command, the UE 104 may reset the MAC and initiate acquiring the target cell’s downlink synchronization. The UE 104 may apply the TA value and start a time alignment timer. The UE 104 may start a handover timer, e.g., a T304 handover failure timer, as described in 3GPP TSs. If the handover timer expires before the handover is complete, the UE may assume that the handover has failed.

The UE 104 may perform the first uplink transmission in the target cell using a dynamic or preallocated uplink grant in the handover command. Receiving the first downlink transmission may implicitly or explicitly indicate the completion of the handover procedure. For example, the first downlink transmission may be a downlink control information (DCI) . When the handover procedure is completed, the UE 104 may stop the handover timer, e.g., the T304 handover failure timer.

During the handover procedure, the UE 104 may obtain the TA value of the target cell 114. For example, the UE 104 may acquire a valid TA value and start a time alignment timer in the target cell during the RACH procedure in the target cell. Different embodiments provide descriptions of UE 104 or network 108 procedures when the time alignment timer expires during the handover procedure.

FIG. 2 illustrates timing alignment 200 in accordance with some embodiments. The signal from a given UE may take some time to reach the base station, which may be referred to as propagation time. For example, a transmission from a given UE at a given distance from the base station may have a propagation time of dT. Consider a common clock between the base station and the UEs in a network. The downlink subframe may start at time S1 from the base station’s point of view (POV) , e.g., the base station may start downlink transmission at time S1. If the UE starts the transmission at S1, the UE’s transmission may be received at the base station at time S1+dT; e.g., the uplink and downlink subframes at the base stations are not aligned in time. However, when the UE starts the transmission at S2 = S1-dT, the UE’s transmission would be received at S2+dT=S1-dT+dT=S1. Therefore, by adding a negative offset of dT to the UE’s transmission, the uplink and downlink subframes may be aligned (up to the timing granularity and accuracy) . Similarly, the downlink transmission started at time S1 may be received by the UE at time S3=S1+dT, assuming that the uplink and downlink propagation time is the same, e.g., dT. In some instances, it is possible that the uplink propagation time differs from the downlink propagation time.

Timing advance is a parameter associated with the timing offset dT., e.g., TA = 2 ·dT. In some instances, the network, e.g., the base station, may estimate the initial TA. The network may send a message to inform the UE about the value of the TA. The base station may estimate the TA during the random access procedure. The UE may send a preamble or other signals on a physical random access channel (PRACH) . For example, the base station may estimate the TA for uplink during UE’s initial access, radio link failure, or during the handover procedure. The base station may send a timing advance command that may include the TA value. For example, the base station may send the TA in a timing advance command using a random access response (RAR) message. Once the UE is connected to the base station, e.g., in an RRC connected state, the base station may keep estimating TA and send timing advance command, e.g., via MAC control element (CE) , to the UE 104.

In some instances, the base station may configure the UE 104 with a timer. The duration of the timer may be associated with the duration during which the UE may assume that the value of the TA is valid. For example, the base station may configure a time alignment timer 235. Time alignment timer 235 may be used to control how long the UE may consider the value of TA to be valid for alignment of the uplink transmission. The duration of the timer may be common among all UEs in the network or may be specific to a UE. The UE may start or restart the time alignment timer 235 based on receiving the timing advance command from the base station. In some instances, when the time alignment timer 235 expires and the UE has not received a new TA value, e.g., via a timing advance command from the base station, the UE may assume that it has lost the uplink synchronization and may initiate a timing-re-alignment procedure, e.g., using the random access procedure.

In response to time alignment timer expiry, the UE may flush all hybrid automatic repeat request (HARQ) buffers and release uplink resources associated with the transmission of reference signals or control information. For example, the MAC sublayer of the UE may notify the RRC layer to release the physical uplink control channel (PUCCH) resources for periodic channel quality indicators (CQIs) , scheduling requests, or sounding reference signals (SRSs) . The UE may also clear configured downlink assignments and uplink grants.

In some embodiments, the time alignment timer 235 associated with the target cell may expire during a RACH-less handover procedure. Releasing some RRC configurations, e.g., configurations not applied to the target cell, may be unnecessary. Also, the time alignment timer may expire after UE’s first transmission but before receiving downlink transmission, e.g., handover acknowledgment. Flushing the HARQ buffer in response to time alignment timer expiry may cause the handover procedure to fail if the network does not receive the UE’s first uplink transmission. In some embodiments, the UE may refrain from flushing the HARQ buffer in response to time alignment timer expiry to allow for retransmission of the UE’s first uplink transmission.

FIG. 3 is a signaling diagram 300 illustrating aspects of RACH-less handover in accordance with some embodiments. The signaling diagram 300 may include operations performed by, and signaling messages transmitted between, the UE 104, the serving base station 102-1, and the target base station 102-2. Operations described with respect to the base stations 102-1 or 102-2 may be performed by one or more components of the network, including, for example, a base station, a gNB, a TRP, an NP, etc. The signaling diagram 300 represents an embodiment in which RACH-less handover is performed.

At 305, the signaling diagram 300 may include one or more handover preparation signalings transmitted between the target cell’s base station 102-2 and the serving cell’s base station 102-1. The handover preparation signaling may include information for preparing the target cell for handover. For example, the serving cell’s base station 102-1 may send a handover request message to the target cell’s base station 102-2. The handover request message may include information associated with the UE, e.g., UE context or security context, as described in 3GPP TSs. The target cell 114 may configure resources for the incoming UE 104, e.g., preallocate uplink resources for the UE’s uplink transmission.

At 310, the serving cell’s base station (serving base station) 102-1 may send a handover command to the UE 104. For example, the handover command may be an RRC signal. The handover command may include timing advance information of the target cell. For example, the handover command may indicate to the UE 104 that the TA value of the target cell is 0. In another example, the handover command may indicate to the UE 104 that the TA value of the target cell is the same as the TA value of the serving cell. The handover command may include an indication of the target cell, e.g., that target cell’s identifier (ID) , such as physical cell ID (PCI) . The handover command may include preallocated uplink resources, e.g., preallocated uplink grant, which may allocate resources or schedule uplink transmission for the UE 104.

After receiving the handover command, the UE 104 may stop transmission to or reception from the serving base station 102-1. In response to the handover command, the UE 104 may initiate RACH-less handover to the target cell. Initiating RACH-less handover may include resetting MAC, e.g., as described in the 3GPP TS 38.321, acquiring downlink synchronization, e.g., as described in signaling at 315 in FIG. 3, applying a TA value, or storing the preallocated uplink grant. The UE 104 may start a time alignment timer or a handover timer, e.g., a T304, as described in the 3GPP TSs. “Applying a configuration, ” e.g., applying an RRC configuration or applying a TA value, may refer to setting up a configuration or modifying an existing configuration based on the configuration being applied. When a configuration is applied, it may mean that the specified settings or parameters have been set and are currently in use. Similarly, if a configuration “is not applied, ” it may mean that the specified setting or parameters have not been set or are not currently in use.

At 315, the UE 104 may detect or receive the synchronization reference signals from the target cell, e.g., transmitted by the target base station 102-2. For example, the UE 104 may detect, receive, or decode the target cell’s primary or secondary synchronization reference signals.

At 320, the UE 104 may send the first uplink transmission. The UE 104 may use the resources associated with the preallocated uplink grant received in the handover command for its first uplink transmission. The UE’s first uplink transmission may be a scheduling request. The UE 104 may store a copy of the first uplink transmission in a HARQ buffer. The UE’s first uplink transmission may implicitly or explicitly indicate the handover completion at UE 104. For example, the UE’s first transmission may include a handover completion message. The target cell may implicitly interpret the UE’s first transmission as an indication of completing the handover procedure at the UE 104.

At 325, the UE 104 may receive a downlink transmission from the target base station 102-2. The downlink transmission at 325 may implicitly or explicitly indicate an acknowledgment that the target base station 102-2 has successfully received the UE’s first uplink transmission. The downlink transmission may be a DCI, e.g., a UE-specific scheduling DCI, as described in the 3GPP TSs. With the completion of the handover at UE 104 and the target base station 102-2, the UE 104 and target base station 102-2 (now the new serving cell or serving base station) may resume data transmission.

The time alignment timer may expire before the completion of the handover or expiration of the handover timer. Depending on whether, at the expiry of the time alignment timer, the UE has already made the first uplink transmission or whether the RRC configurations of the target cell have been applied, the UE may determine whether to flush the HARQ buffer, fall back on RACH-based handover procedure, or keep or release the RRC configuration.

FIG. 4 is a signaling diagram 400 illustrating aspects of RACH-less handover in accordance with some embodiments. The signaling diagram 400 may include operations performed by, and signaling messages transmitted between, the UE 104, the serving base station 102-1, and the target base station 102-2. Operations described with respect to the base stations 102-1 or 102-2 may be performed by one or more components of the network, including, for example, a base station, a gNB, a TRP, an NP, etc. The signaling diagram 300 represents an embodiment in which RACH-less handover is performed. Except as otherwise described, operations of the signaling diagram 400 may be similar to like-named operations of the signaling diagram 300.

Signaling diagram 400 differs from signaling diagram 300 due to a variation in the expiration of the time alignment timer. In particular, signaling diagram 400 includes, at 415, the time alignment timer may expire before the expiration of the handover timer. The UE 104 may apply one of the following two options.

In option one, the UE may keep or maintain the RRC configuration of the target cell. In one embodiment, the UE 104 may keep or maintain the RRC configuration of the target cell if it is not applied. For example, the PUCCH and SRS configurations may not be applied before the RACH-less handover completion. The UE 104 may keep or maintain the RRC configuration associated with the PUCCH and SRS of the target cell after the time alignment timer expiry.

In one embodiment, the time alignment timer is a timeAligmentTimer as described in the 3GPP TSs. The MAC layer may suppress a release indicaiton to the RRC layer. The release indication may indicate releasing the RRC configuration of the target cell. When a timeAlignmentTimer expires, if the timeAlignmentTimer is associated with a primary timing advance group (PTAG) , the UE 104 may: flush all HARQ buffer for all serving cells; notify RRC to release PUCCH for all serving cells, if configured, and if it is not during RACH-less handover, e.g., suppressing the notification to the RRC if the notification is triggered by the expiration of the time alignment timer during RACH-less handover; notify RRC to release SRS for all serving cells, if configured, and if it is not during RACH-less handover, e.g., suppressing the notification to the RRC if the notification is triggered by the expiration of the time alignment timer during RACH-less handover; clear any configured downlink assignment and configured uplink grants; clear any PUSCH resource for semi-persistent CSI reporting; consider all running timeAlignmentTimersas expired; and maintain the parameters associated with all timing advance groups (TAGs) , e.g., N_TA, as defined in the 3GPP TS 38.211 v. 17.6.0 2023-09-28. A timing advance group (TAG) may include one or more serving cells with the same uplink TA and the same downlink timing reference cell. When a TAG contains the primary cell (PCell) , it is named the primary timing advance group (PTAG) . Upon the expiry of the time alignment timer, the MAC sublayer may not notify the RRC to release RRC configurations, e.g., PUCCH or SRS configurations, during the RACH-less handover.

In one embodiment, upon receiving a PUCCH release request from lower layers, e.g., MAC sublayer, for all bandwidth parts of an indicated serving cell, the UE 104 may release the applied PUCCH channel state information (CSI) resources configured, e.g., by RRC CSI-ReportConfig information element (IE) ; and release the applied scheduling request resource configuration instances, e.g., configured by RRC SchedulingRequestResourceConfig instances in RRC PUCCH-Config IE. Upon receiving an SRS release request from lower layers, e.g., from the MAC sublayer, for all bandwidth parts of an indicated serving cell, the UE 104 may release the applied SRS resource instances, e.g., the RRC SRS-Resource instances configured in RRC SRS-Config IE. Upon receiving a positioning SRS configuration for an RRC inactive state release request from lower layers, e.g., the MAC sublayer, the UE 104 may release the configured and applied RRC srs-PosRRC-Inactive IE. The RRC layer may only release the configurations that have been applied. The RRC layer may keep or maintain the configurations that have not been applied.

In option two, when the time alignment timer expires before the handover timer expiry, the UE 104 may release the RRC configuration. The network may need to know whether the UE 104 maintains or releases the RRC configuration. In one embodiment, the network may configure the UE 104 to maintain or release the RRC configuration upon the expiration of the time alignment timer. For example, the network may use MAC CE or RRC signaling to configure the UE 104. The MAC CE or RRC may include an indication to maintain or release the RRC configuration upon the time alignment timer expiration.

In one embodiment, during the RACH-less handover, the network, e.g., any of the serving base station 102-1, target base station 102-2, core network, or other network elements, may maintain a timer associated with the UE’s time alignment timer. The network may use this timer to determine whether the time alignment timer has expired at the UE 104.

In one embodiment, as the UE’s first transmission, the network may receive signaling associated with a random access procedure, e.g., RACH procedure, from the UE 104 in the target cell. Based on the received signals being UE’s first transmission and the first transmission being associated with a random access procedure, the network may determine that the UE 104 has released the configurations.

In one embodiment, before the expiration of the handover timer, the UE 104 may send an indication in the target cell to inform the network that the time alignment timer has expired or the configuration is released. This message may implicitly or explicitly indicate that the handover procedure at the UE 104 is complete. The UE 104 may use MAC CE, a physical (PHY) layer signaling, or an indication in the handover complete message to carry the indicator. For example, at 420, the UE may send a handover-complete message to the target base station 102-2, including an indication associated with the time alignment timer expiry. In another example, the indication may be associated with releasing the configurations.

When the network identifies the UE 104 has released the RRC configuration, the network may reconfigure the UE 104 after handover completion. For example, at 425, the network may reconfigure the UE 104, e.g., by RRC reconfiguration signaling.

FIG. 5 is a signaling diagram 500 illustrating aspects of RACH-less handover in accordance with some embodiments. The signaling diagram 500 may include operations performed by, and signaling messages transmitted between, the UE 104, the serving base station 102-1, and the target base station 102-2. Operations described with respect to the base stations 102-1 or 102-2 may be performed by one or more components of the network, including, for example, a base station, a gNB, a TRP, an NP, etc. The signaling diagram 300 represents an embodiment in which RACH-less handover is performed. Except as otherwise described, operations of the signaling diagram 500 may be similar to like-named operations of the signaling diagram 400.

Signaling diagram 500 differs from signaling diagram 400 due to a variation in the expiration of the time alignment timer. In particular, signaling diagram 500 includes, at 515, the time alignment timer may expire before the expiration of the handover timer. In some instances, when the time alignment timer expires before the handover timer expires, the UE 104 may not have initiated the first uplink transmission, and the HARQ buffer may be empty. Upon expiration of the time alignment timer at 515, the UE 104 may suspend or abstain from monitoring the downlink control channel. For example, the UE 104 may abstain from monitoring the UE-specific dynamic grant in the target cell. The UE may assume that the preallocated uplink grant received in the handover command is invalid or may release the preallocated uplink grant.

The UE 104 may initiate a random access procedure, e.g., RACH procedure 520, in the target cell. The RACH procedure 520 may be based on the random access procedure described above or in the 3GPP TSs. One of the messages, e.g., random access preamble or message 3, may implicitly or explicitly indicate to the target cell, e.g., the target base station 102-2, handover completion at the UE 104.

FIG. 6 is a signaling diagram 600 illustrating aspects of uplink UE aggregation in accordance with some embodiments. The signaling diagram 600 may include operations performed by, and signaling messages transmitted between, the UE 104, the serving base station 102-1, and the target base station 102-2. Operations described with respect to the base stations 102-1 or 102-2 may be performed by one or more components of the network, including, for example, a base station, a gNB, a TRP, an NTN device, etc. The signaling diagram 300 represents an embodiment in which RACH-less handover is performed. Except as otherwise described, operations of the signaling diagram 600 may be similar to like-named operations of the signaling diagram 300.

Signaling diagram 600 differs from signaling diagram 300 due to a variation in the expiration of the time alignment timer. In particular, signaling diagram 600 includes, at 620, the UE 104 process and sends its first uplink transmission to the target base station 102-2 before the time alignment timer expiration. The UE’s first uplink transmission may implicitly or explicitly indicate to the target base station 102-2 the completion of the handover at UE 104. The UE 104 may store a copy of the first uplink transmission in a HARQ buffer. The target base station 102-2 may not successfully receive or process the UE’s first uplink message.

At 625, the time alignment timer may expire after processing and transmitting the UE’s first uplink transmission. When the time alignment timer expires, the UE 104 may flush the HARQ buffer, e.g., discard the stored copy of the UE’s first uplink transmission and fall back to RACH-based handover.

The UE 104 may initiate a random access procedure, e.g., RACH procedure 630, in the target cell. The RACH procedure 630 may be based on the random access procedure described above or in the 3GPP TSs. One of the messages, e.g., random access preamble or message 3, may implicitly or explicitly indicate to the target cell, e.g., the target base station 102-2, the completion of the handover at the UE 104.

FIG. 7 is a signaling diagram 700 illustrating aspects of uplink UE aggregation in accordance with some embodiments. The signaling diagram 700 may include operations performed by, and signaling messages transmitted between, the UE 104, the serving base station 102-1, and the target base station 102-2. Operations described with respect to the base stations 102-1 or 102-2 may be performed by one or more components of the network, including, for example, a base station, a gNB, a TRP, an NP, etc. The signaling diagram 300 represents an embodiment in which RACH-less handover is performed. Except as otherwise described, operations of the signaling diagram 700 may be similar to like-named operations of the signaling diagram 600.

Signaling diagram 700 differs from signaling diagram 600 due to a variation in the expiration of the time alignment timer. In particular, signaling diagram 700 includes, at 725, time alignment timer expiration. When the time alignment timer expires, the UE 104 maintains the HARQ buffer and does not flush it.

In one embodiment, the UE 104 may assume that the network may receive the first uplink transmission, sent at 620, and wait for the network’s response. The network response may include a handover acknowledgment, a retransmission schedule, or a downlink control information. The network response on the target cell to the UE 104 may indicate that the handover is successfully completed, even if the first uplink transmission is not successfully received by the target base station 102-2.

In one embodiment, the UE 104 may receive and process a retransmission schedule message from the target base station 102-2. The UE 104 may assume that the TA is still valid (despite the expiration of the time alignment timer) and may perform the retransmission. Alternatively, the UE may assume that the TA is invalid and initiate a random access procedure, e.g., a RACH procedure, to obtain a valid TA and to provide the handover complete message to the target cell.

In some embodiments, at 725 and upon expiration of the time alignment timer, the UE 104 may start a wait timer, having a T-wait duration. The UE 104 may wait for an acknowledgment from the target base station 102-2, indicating the handover is complete. If the UE 104 receives a handover acknowledgment before the expiration of the wait timer, then the handover was successfully completed, and the UE 104 may stop the wait timer and handover timer. For example, at 730, the UE 104 may process and receive a downlink transmission, e.g., a DCI. The DCI may indicate to the UE 104 that the handover was successfully completed.

In some embodiment, at 735, the wait timer may expire. Upon the expiration of the wait timer, if the UE 104 has not received handover acknowledgment from the target base station 102-2, the UE 104 may initiate a random access procedure. The UE 104 may initiate a random access procedure, e.g., RACH procedure 740, in the target cell. The RACH procedure 740 may be based on the random access procedure described above or in the 3GPP TSs. One of the messages, e.g., random access preamble or message 3, may implicitly or explicitly indicate to the target cell, e.g., the target base station 102-2, the completion of the handover at the UE 104.

FIG. 8 illustrates an operational flow/algorithmic structure 800 in accordance with some embodiments. The operation flow/algorithmic structure 800 may be performed or implemented by a UE such as, for example, the target UE 104 or UE 1000; or components thereof, for example, baseband processor circuitry 1004A.

The operation flow/algorithmic structure 800 may include, at 810, maintaining a connected state with a serving cell. The connected state may be an RRC connected state. While in an RRC connected state with a serving cell, the UE and the network may perform handover and transfer its connection from a serving cell to a target cell. Maintaining an RRC connected state may include performing measurements, processing and sending measurement reports to the base station.

The operation flow/algorithmic structure 800 may include, at 820, processing a handover command. The UE may receive and process a handover command from the base station of the serving cell. The handover command may include an indication of the target cell, a TA associated with the target cell, or preallocated uplink resources, e.g., a preallocated uplink grant. The UE may initiate a handover procedure in response to the handover command. The handover procedure may be a RACH-less handover procedure. The handover command may indicate a RACH-less handover procedure. For example, the handover command may be an RRC reconfiguration with synchronization message.

The operation flow/algorithmic structure 800 may include, at 830, processing a configuration of a target cell. The configuration may be an RRC configuration of the target cell. The RRC configuration of the target cell may include PUCCH, scheduling request, or SRS configuration.

The operation flow/algorithmic structure 800 may include, at 840, starting a timer associated with a timing alignment. The UE may start a time alignment timer. While the time alignment timer is running, the UE may assume that the value of the uplink TA is valid. The UE may also start a handover timer. When the handover timer expires, the UE may assume that the handover failed. The UE may perform the cell search, cell selection, and initial access procedure to the selected cell.

The operation flow/algorithmic structure 800 may include, at 850, determining that the timer is expired. The UE may determine that the time alignment timer has expired. In some embodiments, the UE may determine that a timing advanced value associated with the time alignement timer is valid even after the expiration of the time alignment timer. The UE may assume that the uplink synchronizaiton state is valid and UE may continue performing uplink transmission.

The operation flow/algorithmic structure 800 may include, at 860, maintaining the target cell’s RRC configuration or releasing the target cell’s RRC configuration. In one instance, the UE may keep or maintain the RRC configuration of the target cell that is not applied. For example, the PUCCH and SRS configuration of the target cell may be considered “not applied” until the handover is completed.

In some instances, the UE may release the RRC configuration. The UE may inform the target base station, and the target base station may reconfigure the released RRC configuration after the completion of the handover.

In some instances, the UE may delay the release of the RRC configuration for some time. When the time alignment timer expires, the UE may start a wait timer. In some embodiments, the UE may start the wait timer after the first uplink transmission.

In some instances, when the time alignment timer expires, the UE may not have initiated the first uplink transmission in the target cell. The UE may flush the HARQ buffer and initiate a RACH-based handover.

In some instances, the time alignment timer expires after the UE’s first uplink transmission in the target cell. The UE’s first transmission may still be in the HARQ buffer when the time alignment timer expires. The UE may flush the HARQ buffer and fall back to RACH-based handover. Alternatively, the UE may keep the HARQ buffer and not flush it and monitor the downlink for a message from the network. The UE may assume that the network may receive the UE’s first uplink transmission in the target cell and wait for the feedback. In another alternative operation, after the UE’s first uplink transmission in the target cell, if there is no downlink transmission from the target cell within a preconfigured time, e.g., T-wait tracked by the wait timer, the UE may trigger a RACH procedure.

Figure 9 illustrates an operational flow/algorithmic structure 900 in accordance with some embodiments. The operation flow/algorithmic structure 900 may be performed or implemented by a network node such as, for example, a node of the network 108 or network node 1100; or components thereof, for example, baseband processor 1104A.

The operation flow/algorithmic structure 900 may include, at 910, sending a configuration of a target cell to a UE. The configuration may be an RRC configuration associated with PUCCH or SRS.

The operation flow/algorithmic structure 900 may include, at 920, maintaining a timer associated with the UE’s time alignment timer. The network may configure and operate a timer that is configured and triggered the same way that the UE’s time alignment timer is configured and triggered.

The operation flow/algorithmic structure 900 may include, at 930, determining whether the UE is to maintain or release the configuration of the target cell. In one example, the network may configure the UE to maintain or release the configuration upon expiration of the time alignment timer. Therefore, based on the expiration of the network timer that is associated with the UE’s time alignment timer, the network may determine whether the UE would maintain or release the configuration.

In another example, the network may receive random access signalings associated with the UE on the target cell. The operation of a random access procedure by the UE on the target cell may indicate to the network that the UE has released the configurations, e.g., the RRC configurations.

In another example, the network may receive a message from the UE that may explicitly indicate whether the UE has maintained or released the configurations.

FIG. 10 illustrates an example UE 1000 in accordance with some embodiments. The UE 1000 may be any mobile or non-mobile computing device, such as, for example, a mobile phone, a computer, a tablet, an industrial wireless sensor (for example, a microphone, a carbon dioxide sensor, a pressure sensor, a humidity sensor, a thermometer, a motion sensor, an accelerometer, a laser scanner, a fluid level sensor, an inventory sensor, an electric voltage/current meter, or an actuator) , a video surveillance/monitoring device (for example, a camera) , a wearable device (for example, a smartwatch) , or an Internet-of-things (IoT) device.

The UE 1000 may include processors 1004, RF interface circuitry 1008, memory/storage 1012, user interface 1016, sensors 1020, driver circuitry 1022, power management integrated circuit (PMIC) 1024, antenna structure 1026, and battery 1028. The components of the UE 1000 may be implemented as integrated circuits (ICs) , portions thereof, discrete electronic devices, or other modules, logic, hardware, software, firmware, or a combination thereof. The block diagram of FIG. 10 is intended to show a high-level view of some of the components of the UE 1000. However, some of the components shown may be omitted, additional components may be present, and different arrangements of the components shown may occur in other implementations.

The components of the UE 1000 may be coupled with various other components over one or more interconnects 1032, which may represent any type of interface circuitry of a processor or a memory, input/output, bus (local, system, or expansion) , transmission line, trace, optical connection, etc. that allows various circuit components (on common or different chips or chipsets) to interact with one another.

The processors 1004 may include processor circuitry such as, for example, baseband processor circuitry (BB) 1004A, central processor unit circuitry (CPU) 1004B, graphics processor unit circuitry (GPU) 1004C, and interface circuitry 1004D. The interface circuitry D may communicatively couple processors 1004 to other components of the UE 1000. The processors 1004 may include any type of circuitry or processor circuitry that executes or otherwise operates computer-executable instructions, such as program code, software modules, or functional processes from memory/storage 1012 to cause the UE 1000 to perform operations such as those described with respect to FIG 7 or elsewhere herein.

In some embodiments, the baseband processor circuitry 1004A may access a communication protocol stack 1036 in the memory/storage 1012 to communicate over a 3GPP-compatible network. In general, the baseband processor circuitry 1004A may access the communication protocol stack to: perform user plane functions at a PHY layer, MAC layer, RLC layer, PDCP layer, SDAP layer, and PDU layer; and perform control plane functions at a PHY layer, MAC layer, RLC layer, PDCP layer, RRC layer, and a non-access stratum layer. In some embodiments, the PHY layer operations may additionally/alternatively be performed by the components of the RF interface circuitry 1008.

The baseband processor circuitry 1004A may generate or process baseband signals or waveforms that carry information in 3GPP-compatible networks. In some embodiments, the waveforms for NR may be based on cyclic prefix OFDM (CP-OFDM) in the uplink or downlink, and discrete Fourier transform spread OFDM (DFT-S-OFDM) in the uplink.

The memory/storage 1012 may include one or more non-transitory, computer-readable media that include instructions (for example, the communication protocol stack 1036) that may be executed by one or more of the processors 1004 to cause the UE 1000 to perform operations such as those described in operation flows/algorithmic structures 800, or otherwise described herein.

The memory/storage 1012 may include any type of volatile or non-volatile memory that may be distributed throughout the UE 1000. In some embodiments, some of the memory/storage 1012 may be located on the processors 1004 themselves (for example, L1 and L2 cache) , while other memory/storage 1012 is external to the processors 1004 but accessible thereto via a memory interface. The memory/storage 1012 may include any suitable volatile or non-volatile memory such as, but not limited to, dynamic random-access memory (DRAM) , static random access memory (SRAM) , erasable programmable read-only memory (EPROM) , electrically erasable programmable read-only memory (EEPROM) , Flash memory, solid-state memory, or any other type of memory device technology.

The RF interface circuitry 1008 may include transceiver circuitry and a radio frequency front module (RFEM) that allows the UE 1000 to communicate with other devices over a radio access network. The RF interface circuitry 1008 may include various elements arranged in transmit or receive paths. These elements may include, for example, switches, mixers, amplifiers, filters, synthesizer circuitry, control circuitry, etc.

In the receive path, the RFEM may receive a radiated signal from an air interface via antenna structure 1026 and proceed to filter and amplify (with a low-noise amplifier) the signal. The signal may be provided to a receiver of the transceiver that down-converts the RF signal into a baseband signal that is provided to the baseband processor of the processors 1004.

In the transmit path, the transmitter of the transceiver up-converts the baseband signal received from the baseband processor and provides the RF signal to the RFEM. The RFEM may amplify the RF signal through a power amplifier prior to the signal being radiated across the air interface via the antenna structure 1026.

In various embodiments, the RF interface circuitry 1008 may be configured to transmit/receive signals in a manner compatible with NR or other access technologies.

The antenna structure 1026 may include antenna elements to convert electrical signals into radio waves to travel through the air and to convert received radio waves into electrical signals. The antenna elements may be arranged into one or more antenna panels. The antenna structure 1026 may have antenna panels that are omnidirectional, directional, or a combination thereof to enable beamforming and multiple-input, multiple-output communications. The antenna structure 1026 may include microstrip antennas, printed antennas fabricated on the surface of one or more printed circuit boards, patch antennas, phased array antennas, etc. The antenna structure 1026 may have one or more panels designed for specific frequency bands, including bands in FR1 or FR2.

The user interface 1016 includes various input/output (I/O) devices designed to enable user interaction with the UE 1000. The user interface 1016 includes input device circuitry and output device circuitry. Input device circuitry includes any physical or virtual means for accepting an input, including, inter alia, one or more physical or virtual buttons (for example, a reset button) , a physical keyboard, keypad, mouse, touchpad, touchscreen, microphones, scanner, headset, or the like. The output device circuitry includes any physical or virtual means for showing information or otherwise conveying information, such as sensor readings, actuator position (s) , or other like information. Output device circuitry may include any number or combinations of audio or visual display, including, inter alia, one or more simple visual outputs/indicators (for example, binary status indicators such as light emitting diodes “LEDs” and multi-character visual outputs, or more complex outputs such as display devices or touchscreens (for example, liquid crystal displays (LCDs) , LED displays, quantum dot displays, projectors, etc. ) , with the output of characters, graphics, multimedia objects, and the like being generated or produced from the operation of the UE 1000.

The sensors 1020 may include devices, modules, or subsystems whose purpose is to detect events or changes in their environment and send the information (sensor data) about the detected events to some other device, module, subsystem, etc. Examples of such sensors include inter alia, inertia measurement units comprising accelerometers, gyroscopes, or magnetometers; microelectromechanical systems or nanoelectromechanical systems comprising 3-axis accelerometers, 3-axis gyroscopes, or magnetometers; level sensors; flow sensors; temperature sensors (for example, thermistors) ; pressure sensors; barometric pressure sensors; gravimeters; altimeters; image capture devices (for example, cameras or lensless apertures) ; light detection and ranging sensors; proximity sensors (for example, infrared radiation detector and the like) ; depth sensors; ambient light sensors; ultrasonic transceivers; microphones or other like audio capture devices; etc.

The driver circuitry 1022 may include software and hardware elements that operate to control particular devices that are embedded in the UE 1000, attached to the UE 1000, or otherwise communicatively coupled with the UE 1000. The driver circuitry 1022 may include individual drivers allowing other components to interact with or control various input/output (I/O) devices that may be present within, or connected to, the UE 1000. For example, driver circuitry 1022 may include a display driver to control and allow access to a display device, a touchscreen driver to control and allow access to a touchscreen interface, sensor drivers to obtain sensor readings of sensors 1020 and control and allow access to sensors 1020, drivers to obtain actuator positions of electro-mechanic components or control and allow access to the electro-mechanic components, a camera driver to control and allow access to an embedded image capture device, audio drivers to control and allow access to one or more audio devices.

The PMIC 1024 may manage the power provided to various components of the UE 1000. In particular, with respect to the processors 1004, the PMIC 1024 may control power-source selection, voltage scaling, battery charging, or DC-to-DC conversion.

In some embodiments, the PMIC 1024 may control, or otherwise be part of, various power-saving mechanisms of the UE 1000. For example, if the platform UE is in an RRC_Connected state, where it is still connected to the RAN node as it expects to receive traffic shortly, then it may enter a state known as Discontinuous Reception Mode (DRX) after a period of inactivity. During this state, the UE 1000 may power down for brief intervals of time and thus save power. If there is no data traffic activity for an extended period of time, then the UE 1000 may transition off to an RRC_Idle state, where it disconnects from the network and does not perform operations such as channel quality feedback, handover, etc. The UE 1000 goes into a very low power state, and it performs paging where again it periodically wakes up to listen to the network and then powers down again. The UE 1000 may not receive data in this state; in order to receive data, it must transition back to RRC_Connected state. An additional power-saving mode may allow a device to be unavailable to the network for periods longer than a paging interval (ranging from seconds to a few hours) . During this time, the device is totally unreachable to the network and may power down completely. Any data sent during this time incurs a large delay, and it is assumed the delay is acceptable.

A battery 1028 may power the UE 1000, although, in some examples, the UE 1000 may be mounted deployed in a fixed location and may have a power supply coupled to an electrical grid. The battery 1028 may be a lithium-ion battery, a metal-air battery, such as a zinc-air battery, an aluminum-air battery, a lithium-air battery, and the like. In some implementations, such as in vehicle-based applications, the battery 1028 may be a typical lead-acid automotive battery.

FIG. 11 illustrates an example network node 1100 in accordance with some embodiments. The network node 1100 may include processors 1104, RF interface circuitry 1108, core network (CN) interface circuitry 1112, memory/storage circuitry 1116, and antenna structure 1126.

The components of the network node 1100 may be coupled with various other components over one or more interconnects 1128.

The processors 1104, RF interface circuitry 1108, memory/storage circuitry 1116 (including communication protocol stack 1110) , antenna structure 1126, and interconnects 1128 may be similar to like-named elements shown and described with respect to FIG. 10.

The processors 1104 may include any type of circuitry, or processor circuitry that executes or otherwise operates computer-executable instructions, such as program code, software modules, or functional processes from memory/storage 1116 to cause the network node 1100 to perform operations such as those described in operation flow/algorithmic structure 900 or otherwise described herein. The interface circuitry 1104D may communicatively couple the processors 1104 to other components of the network node 1100.

The CN interface circuitry 1112 may provide connectivity to a core network, for example, a 5^th Generation Core network (5GC) using a 5GC-compatible network interface protocol such as carrier Ethernet protocols or some other suitable protocol. Network connectivity may be provided to/from the network node 1100 via a fiber optic or wireless backhaul. The CN interface circuitry 1112 may include one or more dedicated processors or FPGAs to communicate using one or more of the aforementioned protocols. In some implementations, the CN interface circuitry 1112 may include multiple controllers to provide connectivity to other networks using the same or different protocols.

It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.

For one or more embodiments, at least one of the components set forth in one or more of the preceding figures may be configured to perform one or more operations, techniques, processes, or methods as set forth in the example section below. For example, the baseband circuitry, as described above in connection with one or more of the preceding figures, may be configured to operate in accordance with one or more of the examples set forth below. For another example, circuitry associated with a UE, base station, or network element as described above in connection with one or more of the preceding figures may be configured to operate in accordance with one or more of the examples set forth below in the example section.

Examples

In the following sections, further exemplary embodiments are provided.

Example 1 includes a method including: maintaining a radio resource control (RRC) connected state with a serving cell; processing a handover command received from the serving cell indicating a handover procedure from the serving cell to a target cell; processing an RRC configuration of a target cell; starting a timer that is associated with a timing alignment; determining the timer is expired; and performing, based on said determining the timer is expired, a first operation or a second operation, wherein: the first operation is to include maintaining the RRC configuration of the target cell based on determining that the RRC configuration of the target cell is not applied or releasing the RRC configuration of the target cell based on determining that the RRC configuration of the target cell is applied, and the second operation is to include releasing the RRC configuration of the target cell.

Example 2 includes the method of example 1 or some other examples herein, wherein the timer is a first timer, and the method further includes: starting a second timer associated with the handover procedure; and determining that the second timer is not expired.

Example 3 includes the method of examples 1 or 2 or some other examples herein, the method further including: processing an indication received from the serving cell; and determining whether to maintain or release the RRC configuration of the target cell based on the indication.

Example 4 includes the method of any of examples 1-3 or some other examples herein, the method further including: generating a message to indicate the timer is expired or the RRC configuration of the target cell is released, the message to be transmitted to the serving cell.

Example 5 includes the method of any of examples 1-4 or some other examples herein, wherein the RRC configuration of the target cell includes a resource associated with a sounding reference signal (SRS) .

Example 6 includes the method of any of examples 1-5 or some other examples herein, wherein said performing comprises performing the first operation, the first operation further includes: suppressing a release message from a medium access control (MAC) layer to an RRC layer, the release message indicating releasing the RRC configuration of the target cell.

Example 7 includes the method of any of examples 1-3 or some other examples herein, the method further includes: generating an uplink message to be transmitted to the target cell before said determining the timer is expired; and storing a copy of the uplink message in a hybrid automatic repeat request (HARQ) buffer.

Example 8 includes the method of any of examples 1-7 or some other examples herein, wherein the handover procedure is a first handover procedure, and the method further includes: determining that a user equipment (UE) has not initiated an uplink transmission; flushing a hybrid automatic repeat request (HARQ) buffer; and initiating a random access procedure associated with a second handover procedure.

Example 9 includes the method of any of examples 1-8 or some other examples herein, wherein the handover command includes a preallocated uplink grant associated with the target cell, and the method further includes: prior to completing the random access procedure, abstaining from monitoring for a UE-specific dynamic grant in the target cell; releasing the preallocated uplink grant; and performing the random access procedure by: generating a random access preamble to be transmitted to the target cell; and generating a random access message, including a handover complete message.

Example 10 includes the method of any of examples 1-9 or some other examples herein, the method further including: flushing a hybrid automatic repeat request (HARQ) buffer; and initiating a random access procedure associated with a second handover procedure.

Example 411 includes the method of any of examples 1-10 or some other examples herein, wherein the handover procedure is a first handover procedure, and the method further includes: starting a wait timer; and monitoring for a downlink message in response to the uplink message.

Example 12 includes the method of any of examples 1-11 or some other examples herein, the method further including: determining that the wait timer is expired; and initiating a random access procedure associated with a second handover procedure.

Example 13 includes a method including: sending a radio resource control (RRC) configuration of a target cell to a user equipment (UE) ; maintaining a timer associated with a time alignment timer of the UE; and determining whether the UE is to maintain or release the RRC configuration of the target cell based on: determining whether the timer is expired; receiving a random access message associated with the target cell; or receiving, from the UE, a message indicating whether the UE is to maintain or release the RRC configuration of the target cell.

Example 13 includes the method of example 12 or some other examples herein, wherein: said determining whether the UE is to maintain or release the RRC configuration of the target cell is based on receiving, from the UE, a message indicating whether the UE is to maintain or release the RRC configuration of the target cell; and the message is a medium access control (MAC) control element (CE) or a physical (PHY) layer signaling.

Example 14 includes the method of examples 12 or 13 or some other examples herein, wherein the method further comprising: determining that the timer is expired; receiving, from the UE, a handover complete message; and sending, to the UE and via the target cell, an RRC reconfiguration signaling.

Example 15 includes the method of any of examples 12-14 or some other examples herein, wherein the method further including: determining that the timer is expired; and receiving, from the UE, a handover complete message.

Another example may include an apparatus comprising means to perform one or more elements of the method described in or related to any of examples 1–15, or any other method or process described herein.

Another example may include one or more non-transitory computer-readable media comprising instructions to cause an electronic device, upon execution of the instructions by one or more processors of the electronic device, to perform one or more elements of the method described in or related to any of examples 1–15, or any other method or process described herein.

Another example may include an apparatus comprising logic, modules, or circuitry to perform one or more elements of the method described in or related to any of examples 1–15, or any other method or process described herein.

Another example may include a method, technique, or process as described in or related to any of examples 1–15, or portions or parts thereof.

Another example may include an apparatus comprising: one or more processors and one or more computer-readable media comprising instructions that, when executed by the one or more processors, cause the one or more processors to perform the method as described in or related to any of examples 1–15, or any other method or process described herein.

Another example may include an apparatus comprising: processing circuitry to perform the method described in or related to any of examples 1–15, or any other method of process described herein; and interface circuitry, coupled with the processing circuitry, the interface circuitry to communicatively couple the processing circuitry to one or more components of a computing platform.

Another example may include a signal as described in or related to any of examples 1–15, or portions thereof.

Another example may include a datagram, information element, packet, frame, segment, PDU, or message as described in or related to any of examples 1–15, or portions thereof, or otherwise described in the present disclosure.

Another example may include a signal encoded with data as described in or related to any of examples 1–15, or portions or parts thereof, or otherwise described in the present disclosure.

Another example may include a signal encoded with a datagram, IE, packet, frame, segment, PDU, or message as described in or related to any of examples 1–15, or portions thereof, or otherwise described in the present disclosure.

Another example may include an electromagnetic signal carrying computer-readable instructions, wherein execution of the computer-readable instructions by one or more processors is to cause the one or more processors to perform the method as described in or related to any of examples 1–15, or any other method of process describe herein.

Another example may include a computer program comprising instructions, wherein execution of the program by a processing element is to cause the processing element to carry out the method described in or related to any of examples 1–15, or any other method of process describe herein.

Another example may include a signal in a wireless network as shown and described herein.

Another example may include a method of communicating in a wireless network as shown and described herein.

Another example may include a system for providing wireless communication as shown and described herein.

Another example may include a device for providing wireless communication as shown and described herein.

Any of the above-described examples may be combined with any other example (or combination of examples) , unless explicitly stated otherwise. The foregoing description of one or more implementations provides illustration and description but is not intended to be exhaustive or to limit the scope of embodiments to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments.

Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Claims

A method comprising:

processing a handover command received from a serving cell indicating a handover procedure from the serving cell to a target cell;

determining a handover without a random access procedure based on the handover command;

starting a timer that is associated with a timing advance value;

determining the timer is expired; and

performing, based on said determining the timer is expired, a first operation or a second operation, wherein:

the first operation is to include releasing a radio resource control (RRC) configuration of the target cell based on determining that the RRC configuration of the target cell is applied, and

the second operation is to include releasing the RRC configuration of the target cell and generating an indication to be sent to the target cell to indicate that the timer is expired or the RRC configuration is released.
The method of claim 1, wherein the handover command includes an indication of the timing advance value or an indication of a preallocated uplink grant.
The method of claim 1, wherein the timer is a first timer, and the method further comprises:

starting a second timer associated with the handover procedure; and

determining that the second timer is not expired.
The method of claim 1, further comprising:

generating a message to indicate the timer is expired or the RRC configuration of the target cell is released, the message to be transmitted to the serving cell.
The method of claim 1, wherein the RRC configuration of the target cell includes a configuration of a physical uplink control channel (PUCCH) , a configuration of a scheduling request, or a configuration of a sounding reference signal (SRS) .
The method of claim 1, wherein said performing comprises performing the first operation, the first operation further comprises:

suppressing a release indication from a medium access control (MAC) layer to an RRC layer, the release indication associated with releasing the RRC configuration of the target cell.
The method of claim 1, further comprising:

generating an uplink message to be transmitted to the target cell before said determining the timer is expired; and

storing a copy of the uplink message in a hybrid automatic repeat request (HARQ) buffer.
The method of claims 1 or 7, the method further comprising:

after said determining that the timer is expied, determining that the timing advance value is valid.
The method of claims 1 or 7, wherein the handover procedure is a first handover procedure, and the method further comprises:

determining that a user equipment (UE) has not initiated an uplink transmission;

flushing a hybrid automatic repeat request (HARQ) buffer; and

initiating a random access procedure associated with a second handover procedure.
The method of claim 9, wherein the handover command includes a preallocated uplink grant associated with the target cell, and the method further comprises:

prior to completing the random access procedure, abstaining from monitoring for a UE-specific dynamic grant in the target cell;

releasing the preallocated uplink grant; and

performing the random access procedure by: generating a random access preamble to be transmitted to the target cell; and generating a random access message, including a handover complete message.
The method of claim 7, further comprising:

flushing a hybrid automatic repeat request (HARQ) buffer; and

initiating a random access procedure associated with a second handover procedure.
The method of claim 7, wherein the handover procedure is a first handover procedure, and the method further comprises:

starting a wait timer; and

monitoring for a downlink message in response to the uplink message.
The method of claim 12, further comprising:

determining that the wait timer is expired; and

initiating a random access procedure associated with a second handover procedure.
An apparatus comprising:

processing circuitry to:

process a handover command received from a serving cell indicating a handover procedure from the serving cell to a target cell;

determine a handover without a random access procedure based on the handover command;

start a timer that is associated with a timing advance value;

determine the timer is expired; and

perform, based on said determining that the timer is expired, a first operation or a second operation, wherein:

the first operation is to include releasing a radio resource control (RRC) configuration of the target cell based on determining that the RRC configuration of the target cell is applied; and

the second operation is to include releasing the RRC configuration of the target cell, and generating an indication to be sent to the target cell to indicate that the timer is expired or the RRC configuration is released.
The apparatus of claim 14, wherein the handover command includes an indication of the timing advance value or an indication of a preallocated uplink grant.
The apparatus of claim 14, wherein the timer is a first timer, and the processing circuitry is further to:

start a second timer associated with the handover procedure; and

determine that the second timer is not expired.
The apparatus of claim 14, wherein the processing circuitry is further to:

generating a message to indicate the timer is expired or the RRC configuration of the target cell is released, the message to be transmitted to the serving cell.
The apparatus of claim 14, wherein the RRC configuration of the target cell includes a configuration of a physical uplink control channel (PUCCH) , a configuration of a scheduling request, or a configuration of a sounding reference signal (SRS) .
The apparatus of claim 14, wherein the processing circuitry is further to:

suppress a release indication from a medium access control (MAC) layer to an RRC layer, the release indication associated with releasing the RRC configuration of the target cell.
The apparatus of claim 14, wherein the processing circuitry is further to:

generate an uplink message to be transmitted to the target cell before said determining the timer is expired; and

store a copy of the uplink message in a hybrid automatic repeat request (HARQ) buffer.
The apparatus of claims 14 or 20, wherein the processing circuitry is further to:

after said determining that the timer is expired, determine that the timing advance value is valid.
The apparatus of claims 14 or 20, wherein:

the handover procedure is a first handover procedure; and

the processing circuitry is further to:

determine that a user equipment (UE) has not initiated an uplink transmission;

flush a hybrid automatic repeat request (HARQ) buffer; and

initiate a random access procedure associated with a second handover procedure.
The apparatus of claim 22, wherein the handover command includes a preallocated uplink grant associated with the target cell, and the processing circuitry is further to:

prior to completing the random access procedure, abstain from monitoring for a UE-specific dynamic grant in the target cell;

release the preallocated uplink grant; and

perform the random access procedure by: generating a random access preamble to be transmitted to the target cell; and generating a random access message, including a handover complete message.
The apparatus of claim 20, wherein the processing circuitry is further to:

flush a hybrid automatic repeat request (HARQ) buffer; and

initiate a random access procedure associated with a second handover procedure.
The apparatus of claim 20, wherein:

the handover procedure is a first handover procedure; and

the processing circuitry is further to:

start a wait timer; and

monitor for a downlink message in response to the uplink message.
The apparatus of claim 25, wherein the processing circuitry is further to:

determine that the wait timer is expired; and

initiate a random access procedure associated with a second handover procedure.
One or more computer-readable media having instructions that, when executed by one or more processors, cause a component of a network node to:

send a radio resource control (RRC) configuration of a target cell to a user equipment (UE) ;

maintain a timer associated with a time alignment timer of the UE; and

determine whether the UE is to maintain or release the RRC configuration of the target cell based on:

determining whether the timer is expired;

receiving a random access message associated with the target cell; or

receiving, from the UE, a message indicating whether the UE is to maintain or release the RRC configuration of the target cell.
The one or more computer-readable media of claim 27, wherein:

said determining whether the UE is to maintain or release the RRC configuration of the target cell is based on receiving, from the UE, a message indicating whether the UE is to maintain or release the RRC configuration of the target cell; and

the message is a medium access control (MAC) control element (CE) or a physical (PHY) layer signaling.
The one or more computer-readable media of claim 27, wherein the instructions, when executed, cause the component of the network node to:

determine that the timer is expired;

receive, from the UE, a handover complete message; and

send, to the UE and via the target cell, an RRC reconfiguration signaling.
The one or more computer-readable media of claim 27, wherein the instructions, when executed, cause the component of the network node to:

determine that the timer is expired; and

receive, from the UE, a handover complete message.