Patent Description:
In a conventional wireless communication network, such as a Long-Term-Evolution (LTE) or evolved LTE (eLTE) network, a handover procedure includes having at least one source base station (e.g., an evolved NodeB (eNB) initiating a handover over an Xn interface through a Handover Request, a target base station performing admission control and providing a radio resource control (RRC) configuration as part of a Handover Acknowledgement, the at least one source base station then providing the RRC configuration to the UE having a Handover Command through RRC signaling, then the UE moving the connection to the target base station.

In the next generation (e.g., <NUM>th Generation New Radio (<NUM> NR), see e.g. <NPL>) wireless communication networks, while network based mobility may be based on similar principles and procedures as those in (e)LTE networks, in order to reduce latency, the Handover Command message may include dedicated random access configuration(s) for contention-free random access procedure. The UE may select a suitable beam from multiple beams of the target cell, and may perform contention-based random access on the UE selected beam if contention-free random access resources are not provided for the UE's selected beam. When dedicated random access configuration is present in the Handover Command message, questions still remain as to how A UE may select the random access resource(s) among dedicated random access configuration(s) and common random access configuration(s) in a multi-beam environment.

<NPL> is concerned with a working group paper on beam selection during handover. Herein, with dedicated RACH resources, the UE can perform contention-free random access procedure, otherwise it would perform CBRA with common RACH resources. After receiving a handover command, the UE can treat the beams with dedicated RACH resources first and select the beam for preamble transmission based on the following criteria. First, the UE can select the first detected one which is above the threshold to perform CBRA when one or multiple beams with dedicated RACH resources <NUM> exist, in this way, RACH procedure is fast and contention-free. Secondly, if RSRP of all the beams would dedicate RACH resources included in the handover command are not above the threshold, the UE may evaluate the beams configured with common RACH resources. The UE can select the first detected one which is above the threshold to perform CBRA when one or multiple beams with common RACH resources exist. If RSRP of all the beams with <NUM> common RACH resources included in the handover command are not above the threshold either, since the UE has already measured all the beams included in the handover command, it can select the best one (the one with the highest RSRP) among them to perform a RACH regarding the best beam is configured with dedicated RACH resources or common RACH resources. If all the beams included in the handover command are not configured with <NUM> dedicated RACH resources, the UE evaluates the beams configured with common RACH resources. It can select the first detected one which is above the threshold to perform CBRA, although RACH is contention-based, preamble transmission via the first detected beam can reduce the latency since the UE does not need to detect and measure more beams, or moreover, RACH can be successful with high possibilities since the beam is above the <NUM> properly set threshold. <NPL>, is a pair from INTERDIGITAL INC. related to beam selection for handover in NR. Herein, if the UE determines that it has at least one suitable (i.e. above a threshold) dedicated PRACH resource associated with CSI-RS, then the UE selects the best corresponding beam for the random access. Otherwise, if the UE determines that it has at least one suitable (i.e., above a <NUM> threshold) dedicated PRACH resource associated with SSB, then the UE selects any of the corresponding beam for the random access. In the latter case, the UE minimizes the latency by selecting the PRACH occasion that occurs earliest in time amongst all resources associated with suitable beams. However, the number of attempts to perform the random access procedure should be controlled by the network. Consequently, the following is proposed: First, the UE performs at most one contention-free random access procedure with a beam associated with a dedicated PRACH resource with CSI-RS upon handover. Secondly, the UE performs at most one contention-free random access procedure with a beam associated with a dedicated PRACH resource with SSB upon handover. Thirdly, the UE performs at most one <NUM> contention-based random access procedure upon handover with a beam associated with the PRACH resource with SSB upon handover.

<NPL> is related to a baseline handover procedure for inter gNB handover in NR. Herein, to avoid additional latency and signaling overhead, beam refinement can be performed before accessing the target cell. The network can use a narrow beam for CSI-RS <NUM> transmission and associate the RACH configurations with the CSI-RS configuration. Then the UE can use cell-specific RACH T/F resources and/or preamble indices associated with CSI- RS configurations to access the target cell. In this case, the handover command can include the association between RACH configurations and CSI-RS configurations. During handover, the UE selects the beam exceeding the threshold and configured with RACH configurations to <NUM> access the target cell. Since association between the RACH configurations and the DL Tx beam may be included in the handover command, the target gNB can determine that DL Tx beam for RAR based on the used resources and/or received preamble. Besides TA value included in RAR, available or best UL beam can also be indicated in UL grant.

Thus, there is a need in the art for random access channel (RACH) resource selection in a multi-beam environment.

The present invention is directed to random access channel (RACH) resource selection in a multi-beam environment. It is defined by the claimed subject-matter. Embodiments not covered by the claimed subject-matter do not form part of the invention.

Aspects of the exemplary disclosure are best understood from the following detailed description when read with the accompanying figures. Various features are not drawn to scale, dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

The following description contains specific information pertaining to exemplary implementations in the present disclosure. The drawings in the present disclosure and their accompanying detailed description are directed to merely exemplary implementations. However, the present disclosure is not limited to merely these exemplary implementations. Other variations and implementations of the present disclosure will occur to those skilled in the art. Unless noted otherwise, like or corresponding elements among the figures may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations in the present disclosure are generally not to scale, and are not intended to correspond to actual relative dimensions.

For the purpose of consistency and ease of understanding, like features are identified (although, in some examples, not shown) by numerals in the exemplary figures. However, the features in different implementations may be differed in other respects, and thus shall not be narrowly confined to what is shown in the figures.

The description uses the phrases "in one implementation," or "in some implementations," which may each refer to one or more of the same or different implementations. The term "coupled" is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The term "comprising," when utilized, means "including, but not necessarily limited to"; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the equivalent.

Additionally, for the purposes of explanation and non-limitation, specific details, such as functional entities, techniques, protocols, standard, and the like are set forth for providing an understanding of the described technology. In other examples, detailed description of well-known methods, technologies, system, architectures, and the like are omitted so as not to obscure the description with unnecessary details.

Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) described in the present disclosure may be implemented by hardware, software or a combination of software and hardware. Described functions may correspond to modules may be software, hardware, firmware, or any combination thereof. The software implementation may comprise computer executable instructions stored on computer readable medium such as memory or other type of storage devices. For example, one or more microprocessors or general purpose computers with communication processing capability may be programmed with corresponding executable instructions and carry out the described network function(s) or algorithm(s). The microprocessors or general purpose computers may be formed of applications specific integrated circuitry (ASIC), programmable logic arrays, and/or using one or more digital signal processor (DSPs). Although some of the exemplary implementations described in this specification are oriented to software installed and executing on computer hardware, nevertheless, alternative exemplary implementations implemented as firmware or as hardware or combination of hardware and software are well within the scope of the present disclosure.

The computer readable medium includes but is not limited to random access memory (RAM), read only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, compact disc read-only memory (CD ROM), magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions.

A radio communication network architecture (e.g., a long term evolution (LTE) system, a LTE-Advanced (LTE-A) system, or a LTE-Advanced Pro system) typically includes at least one base station, at least one user equipment (UE), and one or more optional network elements that provide connection towards a network. The UE communicates with the network (e.g., a core network (CN), an evolved packet core (EPC) network, an Evolved Universal Terrestrial Radio Access network (E-UTRAN), a Next-Generation Core (NGC), <NUM> Core Network (5GC), or an internet), through a radio access network (RAN) established by the base station.

It should be noted that, in the present application, a UE may include, but is not limited to, a mobile station, a mobile terminal or device, a user communication radio terminal. For example, a UE may be a portable radio equipment, which includes, but is not limited to, a mobile phone, a tablet, a wearable device, a sensor, or a personal digital assistant (PDA) with wireless communication capability. The UE is configured to receive and transmit signals over an air interface to one or more cells in a radio access network.

A base station may include, but is not limited to, a node B (NB) as in the UMTS, an evolved node B (eNB) as in the LTE-A, a radio network controller (RNC) as in the UMTS, a base station controller (BSC) as in the GSM/GERAN, an NG-eNB as in an E-UTRA base station in connection with the 5GC, a next generation node B (gNB) as in the <NUM>-RAN, and any other apparatus capable of controlling radio communication and managing radio resources within a cell. The base station may connect to serve the one or more UEs through a radio interface to the network.

A base station may be configured to provide communication services according to at least one of the following radio access technologies (RATs): Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile communications (GSM, often referred to as <NUM>), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, often referred to as <NUM>) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), LTE, LTE-A, eLTE (evolved LTE), New Radio (NR, often referred to as <NUM>), and/or LTE-A Pro. However, the scope of the present application should not be limited to the above mentioned protocols.

The base station is operable to provide radio coverage to a specific geographical area using a plurality of cells forming the radio access network. The base station supports the operations of the cells. Each cell is operable to provide services to at least one UE within radio coverage of the cell. More specifically, each cell (often referred to as a serving cell) provides services to serve one or more UEs within the cell's radio coverage, (e.g., each cell schedules the downlink and optionally uplink resources to at least one UE within the cell's radio coverage for downlink and optionally uplink packet transmissions). The base station can communicate with one or more UEs in the radio communication system through the plurality of cells. A cell may allocate sidelink (SL) resources for supporting proximity service (ProSe). Each cell may have overlapped coverage areas with other cells.

As discussed above, the frame structure for NR is to support flexible configurations for accommodating various next generation (e.g., <NUM>) communication requirements, such as eMBB, mMTC, and URLLC, while fulfilling high reliability, high data rate and low latency requirements. The orthogonal frequency-division multiplexing (OFDM) technology as agreed in 3GPP may serve as a baseline for NR waveform. The scalable OFDM numerology, such as the adaptive sub-carrier spacing, the channel bandwidth, and the Cyclic Prefix (CP) may be also used. Additionally, two coding schemes are considered for NR: (<NUM>) low-density parity-check (LDPC) code and (<NUM>) Polar Code. The coding scheme adaption may be configured based on the channel conditions and/or the service applications.

Moreover, it is also considered that in a transmission time interval TX of a single NR frame, a downlink (DL) transmission data, a guard period, and an uplink (UL) transmission data should at least be included, where the respective portions of the DL transmission data, the guard period, the UL transmission data should also be configurable, for example, based on the network dynamics of NR. In addition, sidelink resource may also be provided in a NR frame to support ProSe services.

According to implementations of the present application, a source base station (e.g., a source gNB) may initiate a handover procedure in response to a measurement report triggered by the measurement configuration(s) set for the UE. As multiple beams in higher frequencies are employed in the next generation wireless communication networks, measurement reports may include beam information, such as beam index(ices) with or without beam measurement results. According to the beam information from the target base station (e.g., a gNB), the target base station may preserve dedicated random access resource(s) by setting the dedicated random access configuration(s) in order for the UE to switch to the target cell. Due to latency of the Xn interface, the most suitable beam(s) of the target cell for the UE may change due to various factors, such as UE's mobility. In some instances, the preserved dedicated random access resource(s) (e.g., beams) may become unusable, such that the UE needs to use common random access resource(s), which may result in delay in the handover procedure and wasting network resources.

For the event-triggered measurement report, the triggering event may be related to whether the cell quality is above (or below) a given cell-level threshold in response to the specified formula. That is, when the corresponding beam information is changed, the source base station would not receive the changed beam information. For example, the measurement report of a neighboring cell A is sent because its cell quality fulfilling the triggering condition. The cell quality of cell A and the related beam information (e.g., beam #<NUM>, which may be identified by SSB or CSI-RS in response to the measurement configuration), are included in the corresponding measurement report. In the beam information, it indicates that beam #<NUM> is the best beam at the time of measurement. The source base station may initiate a handover procedure with a target base station in response to the measurement report, and the target base station may preserve dedicated random access resource(s) associated with beam #<NUM> for fast access. However, due to the UE mobility, when the source base station receives the Handover Command, for example, via a non-ideal Xn interface, and transmits the synchronous reconfiguration (e.g., ReconfigurationWithSync including parameters for synchronous reconfiguration to the target SpCell) contained in the Handover Command to the UE, the UE may have moved to the coverage of another beam (e.g., beam #<NUM>). According to dedicated random access configuration(s), the UE would attempt to perform the random access procedure via the dedicated random access resource(s) associated with beam #<NUM> first. Then, the UE may try to perform the random access procedure via common random access resources(s) of other (detectable) beam(s) being it is able to switch to the target cell, or else the UE would have to trigger an RRC Connection Re-establishment procedure due to the expiration of a configured timer (similar to timer T304 as in LTE).

Implementations of the present application substantially eliminate the situation where the source base station and/or the target base station do not know that the beam information is no longer valid.

Implementations of the present application allow a measurement report to be triggered by beam information change, thereby increasing the success rate of the Handover procedure while allowing beam refinement.

In some implementations, a source base station transmits the measurement configurations to indicate the measurement objects and the associated report configurations. When the source base station desires to trigger the measurement report based on beam information change, a new information element (IE) "ReportOnBeamInfoChanged" is set to true. It should be noted that the "ReportOnBeamInfoChanged" IE may only apply for the cell(s) that still fulfill the triggering condition and not fulfill the leave condition. The triggered cell may fulfill the leave condition later and will be considered as a non-triggered cell afterward. In such a case, the UE does not report any changed beam information for the non-triggered cell.

In some implementations, when the "ReportOnBeamInfoChanged" IE is set to true, it may mean that when the reported beam(s) is changed compared to the previous measurement report, a new measurement report with new beam information may be triggered and sent to the source base station. In the measurement configuration(s), the network may set the parameter X for SSB(s) or the parameter Yfor CSI-RS(s) to indicate the maximum number of beam index(ices) to be reported, in a descending order in response to the beam measurement result(s), where the qualities of the beams are above the predetermined threshold. For example, if in the previous event-triggered measurement report, the reported beam index is #<NUM>. However, when the UE determines that the best beam has changed to beam #<NUM> for the same triggered cell, based on new beam measurements, then a new measurement report with new cell quality and the new reported beam index is sent to the source base station.

In some implementations, when the "ReportOnBeamInfoChanged" IE is set to true, it may mean that when the beam information is entirely different from what's in the previous measurement report, a new measurement report with new beam information may be triggered and sent to the source base station. For example, if in the previous event-triggered measurement report, the reported beam indices are #<NUM> and #<NUM>. However, the UE determines that for the same triggered cell, the reported beam indices (e.g., a new set of best beam indices) are now #<NUM> and #<NUM>, based on new beam measurements, then a new measurement report with the new cell quality and new beam information is reported to the source base station.

In some implementations, when the "ReportOnBeamInfoChanged" IE is set to true, it may mean that when the reported beam set (e.g., a new set of best beams indices) is not the same as the previous reported beam set, a new measurement report with the new beam information may be triggered and sent to the source base station. For example, in the previous event-triggered measurement report, the reported beam indices are #<NUM> and #<NUM>. However, the UE determines that, for the same triggered cell, the reported beam indices (e.g., a new set of best beam indices) are now #<NUM> and #<NUM>, based on new beam measurements, then a new measurement report with new cell quality and new beam information may not need to be reported to the source base station. __In another example, in the previous event-triggered measurement report, the reported beam indices are #<NUM> and #<NUM>. However, the UE determines that, for the same triggered cell, the reported beam indices (e.g., a new set of best beam indices) are now #<NUM> and #<NUM>, based on new beam measurements, then the new measurement report with new cell quality and new beam information may be reported to the source base station.

The following are various implementations to increase the hit rate of dedicated random access resource(s), by setting the new "ReportOnBeamInfoChanged" IE to get the latest beam information.

In Case <NUM>-<NUM>, the source base station keeps updating the beam information to the target base station (if necessary) before the source base station receives the Handover Acknowledgment. As discussed in detail below, in Case <NUM>-<NUM>-<NUM>, the source base station keeps updating the beam information without Handover Request ID. In Case <NUM>-<NUM>-<NUM>, the source base station keeps updating the beam information with Handover Request ID (e.g., accept case). In Case <NUM>-<NUM>-<NUM>, the source base station keeps updating the beam information with Handover Request ID (e.g., suspend case).

In Case <NUM>-<NUM>, when new beam information of the triggered cell is received, the source base station waits for the Handover Acknowledgement in response to the original handover request, and suspends the Handover Command to the UE. Then, the source base station initiates another handover request with new beam information. As discussed in detail below, under Case <NUM>-<NUM>, the base station sends a new Handover Request with new beam information only after receiving a Handover acknowledgement (ACK)/non-acknowledgement (NACK).

In Case <NUM>-<NUM>, when the target base station is able to allocate dedicated random access resources aggressively such that the source base station could indicate both UE and the target base station where the dedicated random access resource(s) are preserved for fast access, (e.g., using a bit map for beams). In this case, once the source base station decides the dedicated random access resource(s) to keep, it would notify the target base station to release the unused dedicated random access resource(s).

As discussed in detail below, in Case <NUM>-<NUM>-<NUM>, the source base station indicates which dedicated random access configuration(s) to use, and notifies the target base station to release the unused dedicated random access configuration(s). In Case <NUM>-<NUM>-<NUM>, the source base station indicates which dedicated random access configuration(s) to use, but doesn't notify the target base station to release the unused dedicated random access configuration(s). In Case <NUM>-<NUM>-<NUM>, the source base station indicates which kind of dedicated random access configuration(s) to use (associated with SSB(s) or CSI-RS(s)), and notifies the target base station to release the unused dedicated random access configuration(s). In Case <NUM>-<NUM>-<NUM>, the source base station indicates which kind of dedicated random access configuration(s) to use (associated with SSB(s) or CSI-RS(s)), but does not notify the target base station to release the unused dedicated random access configuration(s).

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure in <FIG> includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, source base station <NUM> does not know which beam information is used by target base station <NUM> for admission control (e.g., action <NUM>). Thus, source base station <NUM> may only send the Handover Command (e.g., action <NUM>) to UE <NUM> as shown in <FIG>.

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, one or more unique IDs are added in the field of the Handover Request message.

When target base station <NUM> transmits the Handover Acknowledgement message back to source base station <NUM>, target base station <NUM> includes the unique ID(s) of which the Handover Request is considered in the field of the Handover Acknowledgement message. Based on the ID(s) in the field of the Handover Acknowledgement message, source base station <NUM> may determine whether the Handover Command message is acceptable or not (e.g., whether target base station <NUM> refers to the latest beam information for admission control). If source base station <NUM> determines that the Handover Command message is acceptable, it transmits the Handover Command message to UE <NUM> as shown in <FIG>.

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, if source base station <NUM> determines that the Handover Command is unacceptable, it may suspend the Handover Command message to UE <NUM>, and may re-transmit a Handover Request message with the latest measurement information.

In some implementations, source base station <NUM> may suspend the Handover Command message, and wait for the Handover Acknowledgement with ID#<NUM> without retransmitting the Handover Request with ID#<NUM> again. In some implementations, source base station <NUM> may activate a timer after sending an updated Handover Request <NUM> to target base station <NUM>. If source base station <NUM> cannot receive an updated Handover Acknowledgement corresponding to the sent updated Handover Request <NUM> when the timer expires, source base station <NUM> may decide whether to transmit the Handover Command contained in the original Handover Acknowledgement, whether to suspend the Handover Command transmission, and/or whether to resent the updated Handover Request again.

In Case <NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>,_source base station <NUM> does not send more than one Handover Request message before receiving the Handover ACK/NACK message.

Even when source base station <NUM> receives new beam information of the triggered cell, it waits for the Handover Acknowledgement in response to the corresponding Handover Request message, and suspends the Handover Command message to UE <NUM>. Then, source base station <NUM> initiates another Handover Request message with the new beam information. In Case <NUM>-<NUM>, no unique ID in the field of Handover Acknowledgement is required as shown in <FIG>.

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In <FIG>, source base station <NUM> transmits the Handover Request message to target base station <NUM> with the latest measurement information (e.g., the best beam #<NUM> and beam #<NUM> in action <NUM>). According to the measurement information, target base station <NUM> may accept the Handover Request message and aggressively set dedicated random access configuration(s) not only associated with beams #<NUM> and #<NUM>, but also associated with the neighboring beams #<NUM> and #<NUM> in anticipation of the possible UE mobility. Once source base station <NUM> receives the Handover Acknowledgement message which indicates that the dedicated random access configuration(s) are allocated associated with beams #<NUM>, #<NUM>, #<NUM>, and #<NUM>, source base station <NUM> may further indicate to UE <NUM> in the Handover Command message in response to the latest measurement report (e.g., the new measurement report triggered by beam information change). In the present implementation, the new measurement report triggered by beam information change indicates that the best beams have changed to beams #<NUM> and #<NUM>. Then, source base station <NUM> may indicate UE <NUM> to use only dedicated random access configuration(s) associated with beams #<NUM> and #<NUM> only in action <NUM>. At the same time, source base station <NUM> may send a dedicated Resource Release message to target base station <NUM> to release dedicated random access configuration(s) associated with the unused beams (e.g., beams #<NUM> and beam #<NUM>) in action <NUM>.

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, the new measurement report triggered by beam information change indicates that the best beams have changed from beams #<NUM> and #<NUM> to beams #<NUM> and #<NUM>. Then, source base station <NUM> may indicate UE <NUM> to use only dedicated random access configuration(s) associated with beams #<NUM> and #<NUM> only, but doesn't send a dedicated Resource Release to target base station <NUM> to release dedicated random access configuration(s) associated to beams #<NUM> and #<NUM>.

In Case <NUM>-<NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In the handover procedure in <FIG>, source base station <NUM> has both available beam measurement information associated to SSB(s) and CSI-RS(s), and sends a Handover Request message to target base station <NUM> with both of the two kinds of beam measurement information for admission control in action <NUM>. After admission control in action <NUM>, target base station <NUM> may transmit a Handover Acknowledgement message having both dedicated random access configuration(s) of SSB(s) and dedicated random access resources of CSI-RS(s) to source base station <NUM> in action <NUM>. In action <NUM>, in response to the latest measurement report, source base station <NUM> may decide to use one of the two kinds of dedicated random access configurations for UE <NUM>. For example, source base station <NUM> may decide to use the dedicated random access configuration(s) of SSB(s) based on the latest measurement report (e.g., the signal strength of the previous target CSI-RS(s) (or the CSI-RS specific beam(s)) indicating bad signal quality). In action <NUM>, source base station <NUM> may indicate UE <NUM> to use only the dedicated random access configuration(s) associated with SSB(s) only. Source base station <NUM> may also send the dedicated Resource Release Message to target base station <NUM> to release the dedicated random access configuration(s) associated with CSI-RS(s) in action <NUM>.

In the handover procedure in <FIG>, source base station <NUM> has both available beam measurement information associated to SSB(s) and CSI-RS(s), and sends a Handover Request message to target base station <NUM> with both of the two kinds of beam measurement information for admission control in action <NUM>. After admission control, target base station <NUM> may transmit a Handover Acknowledgement message having both dedicated random access configuration(s) of SSB(s) and dedicated random access resources of CSI-RS(s) to source base station <NUM> in action <NUM>. In action <NUM>, in response to the latest measurement report, source base station <NUM> may decide to use one of the two kinds of dedicated random access configurations for UE <NUM>. _For example, source base station <NUM> may decide to use the dedicated random access configuration(s) of SSB(s) based on the latest measurement report (e.g., the signal strength of the previous target CSI-RS(s) (or the CSI-RS specific beam(s)) indicating bad signal quality). In action <NUM>, source base station <NUM> may indicate UE <NUM> to use only the dedicated random access configuration(s) associated with SSB(s) only. Source base station <NUM> does not send the dedicated Resource Release Message to target base station <NUM> to release the dedicated random access resource associated to CSI-RS(s).

In the next generation (e.g., 5GNR) wireless communication networks, system information may be the same across a large area. For example, system information associated to system access (e.g. random access configuration during state transitions) may be the same in a large area. How to communicate information related to common random access configuration(s) to UEs during a handover procedure may present challenges, since UEs are not required to read the SI during handover procedure. In some implementations of the present application, a target base station doesn't need to provide common random access configuration(s) to a UE in the synchronous reconfiguration (e.g., ReconfigurationWithSync). In some implementations of the present application, a source base station is to mandatorily transmit its common random access configuration(s) to the target base station for verification.

In Case <NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, if target base station <NUM> verifies that common random access configuration(s) is the same, it does not provide common random access configuration(s) in the synchronous reconfiguration (e.g., ReconfigurationWithSync) to UE <NUM> in action <NUM>. Once UE <NUM> receives the synchronous reconfiguration (e.g., ReconfigurationWithSync) without common random access configuration(s), it may directly use the stored common random access configuration(s) for switching to the new cell without checking for additional system information in action <NUM>.

In Case <NUM>-<NUM>, <FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, if target base station <NUM> verifies that the common random access configuration(s) is different in action <NUM>, it provides common random access configuration(s) in the synchronous reconfiguration (e.g., ReconfigurationWithSync) to UE <NUM> in action <NUM>. Once UE <NUM> receives the synchronous reconfiguration (e.g., ReconfigurationWithSync) with the common random access configuration(s), it may directly use the new common random access configuration(s) for switching to the new cell in action <NUM>.

For fast access, dedicated random access configuration(s) (or resource(s)) shall be prioritized to use for access to the target cell, which is contention-free. However, if the UE is unable to (e.g., dedicated random access resources are not configured) or fails to use dedicated random access resources to access the target cell (if dedicated random access resources are configured), it should consider fallback options, such as using common random access configuration(s) (or resource(s)) to access the target cell before triggering the RRC Connection Re-establishment procedure. It should be noted that the dedicated random access resource could be associated to a SSB or a CSI-RS.

The problem is how and when a UE can determine that all dedicated random access resources are unable to be used or fail to complete the random access procedure to the target cell. There are two aspects to be considered, e.g., the quality of the associated beam and the number of times of access try. The target base station may provide a threshold for the beam(s) associated with the dedicated random access resource(s). Also, the target base station may provide a maximum number K of access try. In addition, for certain services, only the finer beams are able to provide the satisfied throughput. Therefore, fallback to use common random access resources may not be feasible. For such a case, the target base station may also indicate the UE whether the common random access resources can be used or not. If the common random access resource cannot be used once all dedicated random access resources are considered (when fulfilled some given criteria), the UE may not directly trigger the re-establishment procedure or notify the source base station by a handover failure information such that the source base station may take the alternative action, e.g., handover to another target base station or target cell by triggering a new handover request.

In various implementations of the present application, multiple preambles may be used for contention-free random access procedure. In this case, a UE may perform multiple continuous preambles with same preamble sequences on different dedicated random access resources of the same beam (with same or different transmission power level), and wait for a single RAR window for response and this would count as <NUM>. It may be UE's implementation on whether it would use multiple random access preambles or not. For example, the UE may decide in response to the received random access resources. Or, the UE may allow to use multiple preambles for contention-free random access procedure by network configurations. For CSI-RS specific beams, UE may need to know the association between dedicated random access resource and the corresponding CSI-RS specific beam.

In the following implementation(s), after admission control, the target base station may transmit a Handover Acknowledge with Handover Command in the container. The Handover Command may include the information of dedicated random access resources, the corresponding threshold for the beam associated with the dedicated random access resources, the maximum number K of random access attempts to try before allowing using common random access resources, and common random access resources allowance, multiple preamble transmission allowance.

The corresponding threshold for the beam associated with the dedicated random access resources is used to determine whether a beam associated to dedicated random access resources is qualified to be used (e.g., using RSRP threshold). Specifically, if the quality of the beam associated to dedicated random access resources is below the threshold, the UE is not allowed to use the corresponding dedicated random access resources to access the target cell. If the threshold is not present, the UE may use the threshold configured for cell quality derivation and beam reporting. In another implementation, the threshold may be always the same as the one configured for cell quality derivation and beam reporting. Thus, the threshold therefore does not need to be provided. In an alternative way, if the threshold is not present, it may depend on the UE implementation to determine the acceptable beam(s) to use random access resource(s).

The maximum number K of access try on dedicated random access resources before allowing using common random access resources may be present when the dedicated random access resources are allocated to the UE for fast access the target cell. There are a number of ways to count the maximum number K. For example, each random access attempt may count as <NUM> no matter each random access attempt is on the same beam or not. In another implementation, continuous random access attempts on the same beam may only count as <NUM>. If K is present, the UE may only evaluate the beams associated with dedicated random access resources. If K is not present or set to infinite and dedicated random access configuration(s) are configured, it means that the UE may use dedicated random access resource(s) to access the target cell without using common random access resource(s) until the timer (e.g., T304, which is used for triggering RRC Connection Re-establishment procedure) expired.

In another implementation, if dedicated random access configuration(s) are configured, the UE may use dedicated random access resource(s) to access the target cell if there is at least one suitable beam (which quality is above the threshold) associated with dedicated random access resource(s). If the UE tries to initiate a random access attempt but there is no suitable beam (which quality is above the threshold) associated with dedicated random access resource(s), the first coming common random access resource(s) of the detectable beam associated with common random access resource(s) may be used for random access attempt. In some implementations, the definition of a detectable beam may the same as a suitable beam (i.e., a beam which quality is above the threshold given for SSB), in response to pre-defined criteria, or left for specific UE implementation(s). It is noted that the SSB-rsrp threshold is configured in random access common configuration and the CSI-RS-rsrp threshold is configured in dedicated random access configuration. Alternatively, if the UE tries to initiate a random access attempt but there is no suitable beam (which quality is above the threshold) associated with dedicated random access resource(s), the common random access resource(s) of the strongest detectable beam associated with common random access resource(s) is used for random access attempt. Even the UE uses common random access resource(s) for random access attempt, it may still use dedicated random access resource(s) again for the next random access attempt if the previous random access attempt on common random access resource(s) fails and there is at least one suitable beam (which quality is above the threshold) associated with dedicated random access resource(s).

Common random access resources allowance is a bit for indicating whether common random access resources can be used or not if the access try on dedicated random access resources exceeds the maximum number K (if present). If the maximum number K is present and the UE is not allowed to use common random access resources to access the target cell, the UE may directly trigger the re-establishment procedure or notify the source base station for new command.

Multiple preamble transmission allowance is used to indicate whether multiple preamble transmission on the dedicated random access resource(s) of the same beam is allowed or not.

<FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, in the Handover Acknowledgement, the Handover Command in the container includes dedicated random access resources, corresponding to threshold for the beam associated with dedicated random access resources, a maximum number K of random access attempts to try before allowing using common random access resources, common random access resources allowance, and multiple preamble transmission allowance, as shown in action <NUM> of <FIG>.

In another implementation, the UE does not need to really perform random access try but to consider the first coming K dedicated random access resources of all beams associated with dedicated random access resource(s) for fast access. If the corresponding threshold for the beam associated with the dedicated random access resources is present, the UE may initiate the random access attempt on the first coming dedicated random access resource(s) of the suitable beam(s) associated with dedicated random access resource(s). If failed, the UE may initiate the random access attempt on the next coming dedicated random access resource(s) of the suitable beam(s) associated with dedicated random access resource(s) is used for random access attempt. The UE may only use the first coming K dedicated random access resources of all beams associated with dedicated random access resource(s). After passing the first K dedicated random access resources of all beams associated with dedicated random access resource(s), the UE may start to use common random access resources to access the target cell.

<FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, in the Handover acknowledgement, the Handover Command in the container includes dedicated random access resources, corresponding to threshold for the beam associated with dedicated random access resources, a maximum number K of the first coming dedicated random access resources to try before allowing using common random access resources, common random access resources allowance, and multiple preamble transmission allowance, as shown in action <NUM> of <FIG>.

In another implementation, a timer T-DR for using dedicated random access resources is configured. After receiving the Handover Command message, the UE may use dedicated random access resource(s) to access the target cell if there is at least one suitable beam (which quality is above the threshold) associated with dedicated random access resource(s) while the timer T-DR is running. If the timer T-DR is expired, the UE is allowed to use common random access resource(s) to access the target cell.

<FIG> illustrates a handover procedure for UE <NUM> to switch from source base station (e.g., source gNB) <NUM> to target base station (e.g., target gNB) <NUM>, where the handover procedure includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In the handover procedure in <FIG>, in the Handover acknowledgement, the Handover Command in the container includes dedicated random access resources, corresponding to threshold for the beam associated with dedicated random access resources, a Timer T-DR, common random access resources allowance, and multiple preamble transmission allowance, as shown in action <NUM> in <FIG>.

In various implantations of the present application, the target base station may include one or more of the random access configurations in the synchronous reconfiguration (e.g., ReconfigurationWithSync) to enable the UE to access the target cell. The random access configurations may include (i) common random access configuration associated with SSB(s), (ii) common random access configuration(s) associated with SSB(s) and dedicated random access configuration(s) associated with SSB(s), (iii) common random access configuration(s) associated with SSB and dedicated random access configuration(s) associated with CSI-RS.

In Case <NUM>-<NUM>-<NUM>, if there are no dedicated random access resource(s) allocated in the Handover Command, the first come first try principle is followed. As shown in <FIG>, for all detectable beams, common random access resource(s) of beam #<NUM> comes first when the UE receives the Handover Command message. Therefore, the UE may perform the random access procedure on common random access resource(s) of beam #<NUM>. If the random access procedure on common random access resource(s) of beam #<NUM> fails (e.g., no corresponding RAR is received within the RAR window), the UE may try to perform the random access procedure on the next coming common random access resource(s) of a certain detectable beam. The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s).

In Case <NUM>-<NUM>-<NUM>, if there are no dedicated random access resource(s) allocated in the Handover Command or the UE falls back to use common random access resources (e.g., after maximum of access try of using dedicated random access resources is reached), common random access resource(s) with the strongest detectable beam is used to access the target cell. Thus, the UE may perform the random access procedure on common random access resource(s) of strongest beam. If the random access procedure on common random access resource(s) of strongest beam fails (e.g., no corresponding RAR is received within the RAR window), the UE may try to perform the random access procedure on the common random access resource(s) of the detectable beam with the second highest quality.

In Case <NUM>-<NUM>-<NUM>, if there are dedicated random access resource(s) associated with NR-SS(s) (or SSB specific beam(s)) allocated in the Handover Command, the first coming dedicated random access resource(s) of all suitable beam(s) associated to dedicated random access resource(s) may be tried first. A suitable beam is one with the quality of the beam associated to dedicated random access resource(s) being above the threshold. In the present implementation, the maximum number K of access try on dedicated random access resources before allowing using common random access resources is <NUM>. As shown in <FIG>, dedicated random access resources of beam #<NUM> comes first among all the suitable beams after the UE receives the Handover Command message. Thus, the UE may perform the random access procedure on dedicated random access resource(s) of beam #<NUM>. If the random access procedure on dedicated random access resource(s) of beam #<NUM> fails (e.g., no corresponding RAR is received within the RAR window), the UE may try to perform the random access procedure on the next coming dedicated random access resources of a suitable beam (which quality is above the threshold), which is beam #<NUM> as shown in <FIG>. In the same implementation, when the UE reaches the maximum number K of access try, before the timer (e.g., T304 timer or the like) is expired (which would trigger the RRC Connection Re-establishment Procedure), the UE is allowed to use common random access resource(s) of all detectable beams to access the target cell (if common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s). At this stage, the first come first try principle may then be followed. Specifically, the UE may perform random access procedure on the first coming random access resource(s) of all detectable beam(s). However, if the next beam the UE tries to access is the one which is associated with dedicated random access resource(s), the UE is still allowed to use dedicated random access resource(s) to access the target cell. It should be noted that when falling back to use common random access Resource(s), the UE may use common random access resource(s) with the strongest detectable beam to access the target cell as introduced in Case <NUM>-<NUM>-<NUM>.

It should be noted that, in other implementations, the UE is not forbidden to still use common random access resource(s) of the detectable beam which is associated dedicated random access resource(s) to access the target cell as shown in <FIG>. This may be left for specific UE implementation(s) or according to the pre-defined rules (e.g., whether it is allowed to use common random access resource after the UE reaches the maximum number K of access try.

In Case <NUM>-<NUM>-<NUM>, similar to Case <NUM>-<NUM>-<NUM>, there are dedicated random access resource(s) associated with NR-SS(s) (or SSB specific beam(s)) allocated in the Handover Command, the first coming dedicated random access resource(s) of all suitable beam(s) associated to dedicated random access resource(s) would be try first. A suitable beam is the quality of the beam associated to dedicated random access resource(s) is above the threshold. However, in this implementation, the maximum number K of the first coming dedicated random access resources to try before allowing using common random access resource is set to <NUM>. If the first <NUM> Dedicate random access Resource(s) have passed, the UE is then allowed to use common random access resource(s) of all detectable beams to access the target cell (if common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s) as shown in <FIG>.

In another implementation, the UE is not forbidden to still use common random access resource(s) of this detectable beam which is associated dedicated random access resource(s) to access the target cell as shown in <FIG>.

In Case <NUM>-<NUM>-<NUM>, similar to Case <NUM>-<NUM>-<NUM>, there are dedicated random access resource(s) associated with NR-SS(s) (or SSB specific beam(s)) allocated in the Handover Command, the first coming dedicated random access resource(s) of all suitable beam(s) associated to dedicated random access resource(s) may be try first. A suitable beam is the quality of the beam associated to dedicated random access resource(s) is above the threshold. But, in this implementation, a timer T-DR for using dedicated random access resources is configured. If the timer T-DR is expired, the UE is then allowed to use common random access resource(s) of all detectable beams to access the target cell (if common random access resources allowance is set to true). The definition of a detectable beam could be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s) as shown in <FIG>.

In another implementation, the UE is not forbidden to still use common random access resource(s) of this detectable beam, which is associated dedicated random access resource(s) to access the target cell as shown in <FIG>.

In Case <NUM>-<NUM>-<NUM>, if there are dedicated random access resources associated with CSI-RS(s) (or CSI-RS specific beam(s)) allocated in the Handover Command message, the first coming dedicated random access resource(s) of all suitable beams associated to dedicated random access resource(s) may be tried first. A suitable beam is that the quality of the beam associated to dedicated random access resource(s) is above the threshold. In the present implementation, the maximum number K of access try on dedicated random access resources before allowing using common random access resources is <NUM>. As shown in <FIG>, dedicated random access resource(s) of beam #A comes first among all the suitable beams after the UE receives the Handover command. Therefore, the UE may perform the random access procedure on dedicated random access resource(s) of beam #A. If the random access procedure on dedicated random access resource(s) of beam #A fails (e.g., no corresponding RAR is received within the RAR window), the UE may try to perform the random access procedure on the next coming dedicated random access resources of a suitable beam (which quality is above the threshold), which is beam #B as shown in <FIG>. In <FIG>, the beam #<NUM> is a wide beam that covers the narrow beam #A and #B.

In the same implementation, when the UE reaches the maximum number K of access try, then, before the timer (e.g., T304 timer or the like) is expired (which would trigger the RRC Connection Re-establishment Procedure), the UE is then allowed to use the common random access resources of all detectable beams to access the target cell (if the common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s). In this stage, the first come first try principle may be followed. Specifically, the UE may perform random access procedure on the first coming random access resource(s) of all detectable beam(s). As shown in <FIG>, the first coming common random access resource(s) of the detectable beam is beam #<NUM>, assuming that beam #<NUM> is not detectable. However, no dedicated random access resources can be used anymore since the UE may already move out of the coverage of the CSI-RS specific beam(s) associated with dedicated random access resources. Note that when falling back to use common random access Resource(s), the UE may use common random access resource(s) with the strongest detectable beam to access the target cell as introduced in Case <NUM>-<NUM>-<NUM>.

In another implementation, when the UE reaches the maximum number K of access try, before the timer (e.g., T304 timer or the like) is expired (which would trigger the RRC Connection Re-establishment Procedure), the UE is allowed to use the common random access resources of all detectable beams to access the target cell (if the common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s). In this stage, the first come first try principle is followed. Specifically, the UE would perform random access procedure on the first coming random access resource(s) of all detectable beam(s). However, the dedicated random access resources may still be used for avoiding contention-based random access procedure. It may be left to specific UE implementation(s), or by network configurations.

In Case <NUM>-<NUM>-<NUM>, similar to Case <NUM>-<NUM>-<NUM>, there are dedicated random access resources associated with CSI-RS(s) (or CSI-RS specific beam(s)) allocated in the Handover Command message, the first coming dedicated random access resource(s) of all suitable beams associated to dedicated random access resource(s) may be tried first. A suitable beam is that the quality of the beam associated to dedicated random access resource(s) is above the threshold. In the present implementation, the maximum number K of the first coming dedicated random access resources to try before allowing using common random access resource is set to <NUM>. When the first <NUM> Dedicate random access Resource(s) have passed, the UE is then allowed to use common random access resource(s) of all detectable beams to access the target cell (if common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s) as shown in <FIG>.

In another implementation, when the first coming K Dedicate random access Resource(s) have passed, the UE may still use dedicated random access resources for avoiding contention-based random access procedure. It may be left to specific UE implementation(s), or by network configurations.

In Case <NUM>-<NUM>-<NUM>, similar to Case <NUM>-<NUM>-<NUM>, there are dedicated random access resources associated with CSI-RS(s) (or CSI-RS specific beam(s)) allocated in the Handover Command message, the first coming dedicated random access resource(s) of all suitable beams associated to dedicated random access resource(s) may be tried first. A suitable beam is that the quality of the beam associated to dedicated random access resource(s) is above the threshold. But, in the present implementation, a timer T-DR for using dedicated random access resources is configured. If the timer T-DR is expired, the UE is then allowed to use common random access resource(s) of all detectable beams to access the target cell (if common random access resources allowance is set to true). The definition of a detectable beam may be the same as a suitable beam, in response to pre-defined criteria, or left for specific UE implementation(s) as shown in <FIG>.

In another implementation, if the timer T-DR is expired, the UE may still use dedicated random access resources for avoiding contention-based random access procedure. It may be left to specific UE implementation(s), or by network configurations.

<FIG> is a flowchart of a method performed by a UE during a handover procedure, according to an example implementation of the present application. As shown in <FIG>, flowchart <NUM> includes actions <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In action <NUM>, the UE, through its processing circuitry, determines whether a contention-free random access resource associated with a first Synchronization Signal Block (SSB) is received. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, the UE, through its processing circuitry, determines whether a first Synchronization Signal-Reference Signal Received Power (SS-RSRP) of the first SSB is greater than a first threshold. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, when the first SS-RSRP of the first SSB is greater than the first threshold, then the UE, through its transmitting circuitry, transmits a random access preamble, by using the contention-free random access resource associated with the first SSB.

In action <NUM>, when the first SS-RSRP of the first SSB is not greater than the first threshold, the UE, through its processing circuitry, determines whether a second Synchronization Signal-Reference Signal Received Power (SS-RSRP) of a second SSB associated with a contention-based random access resource is greater than the first threshold. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, when the second SS-RSRP of the second SSB associated with the contention-based random access resource is greater than the first threshold, the UE, through its transmitting circuitry, transmits the random access preamble, by using the contention-based random access resource associated with the second SSB.

In action <NUM>, when the outcome of determination of action <NUM> is No, the UE determines whether a contention-free random access resource associated with a channel state information reference signal (CSI-RS) is received. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, when the contention-free random access resource associated with the CSI-RS is received, the UE, through its processing circuitry, determines whether a Channel State Information-Reference Signal Received Power (CSI-RSRP) of the CSI-RS is greater than a second threshold. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, when the CSI-RSRP of the CSI-RS is greater than the second threshold, the UE, through its transmitting circuitry, transmits the random access preamble by using the contention-free random access resource associated with the CSI-RS.

In action <NUM>, when the contention-free random access resource associated with CSI-RS is received, or when the CSI-RSRP of the CSI-RS is not greater than the second threshold, the UE, through its processing circuitry, determines whether a second SS-RSRP of a second SSB associated with a contention-based random access resource is greater than the first threshold. If the outcome of determination of action <NUM> is Yes, flowchart <NUM> proceeds to action <NUM>. If the outcome of determination of action <NUM> is No, flowchart <NUM> proceeds to action <NUM>.

In action <NUM>, when the outcome of determination of action <NUM> or <NUM> is No, the UE, through its transmitting circuitry, transmits the random access preamble, by using any SSB with common random access resource. In some implementations, the UE may not consider the first threshold when selecting the SSB in action <NUM>.

It should be noted that flowchart <NUM> in <FIG> describes a random access selection mechanism during a random access procedure. However, in random access procedure, the random access selection mechanism may be triggered several times, for example, based on the response from the network.

<FIG> is a flowchart of a method performed by a UE for iteration of random access resource selections during a handover procedure, according to an example implementation of the present application. In <FIG>, flowchart <NUM> includes actions <NUM> and <NUM>.

In action <NUM>, the UE transmits a first random access preamble, by using a contention-based random access resource associated with a SSB, during a random access procedure. In the present implementation, action <NUM> may correspond to action <NUM> or <NUM> in <FIG>. That is, during the first random access attempt, the UE first attempts to select dedicated random access resource(s) associated with a SSB (e.g., the first SSB above the first threshold in <FIG>) to transmit the first random access preamble, but was not successful in doing so. Then, the UE attempts to transmit the first random access preamble, by selecting a contention-based random access resource associated with another SSB (e.g., the second SSB above the second threshold in <FIG>), during the first random access attempt. In action <NUM>, the UE is able to transmit the first random access preamble, by using the contention-based random access resource associated with the SSB (e.g., the second SSB above the second threshold in <FIG>), during a random access procedure.

In action <NUM>, during the same random access procedure, when there is another random access attempt (e.g., a second random access attempt), the UE may determine whether another contention-free random access resource is greater than the first threshold or the second threshold for transmitting another random access preamble. That is, even when the UE has used common random access resource(s) for a random access attempt during a random access procedure, the UE may, in a subsequent random access selection iteration during the same random access procedure, use dedicated random access resource(s) for the next random access attempt, even after the previous random access attempt on dedicated random access resource(s) failed, but there is at least one suitable beam(s) (whose quality is above the first threshold) associated with dedicated random access resource(s) available. Effectively, with reference to <FIG>, after action <NUM> or <NUM>, when another access attempt arises, the UE may start the random access selection mechanism again from action <NUM> in flowchart <NUM>.

<FIG> illustrates a block diagram of a node for wireless communication, in accordance with various aspects of the present application. As shown in <FIG>, a node <NUM> may include a transceiver <NUM>, a processor <NUM>, a memory <NUM>, one or more presentation components <NUM>, and at least one antenna <NUM>. The node <NUM> may also include an RF spectrum band module, a base station communications module, a network communications module, and a system communications management module, input/output (I/O) ports, I/O components, and power supply (not explicitly shown in <FIG>). Each of these components may be in communication with each other, directly or indirectly, over one or more buses <NUM>. In one implementation, the node <NUM> may be a UE or a base station that performs various functions described herein, for example, with reference to <FIG>.

The transceiver <NUM> having a transmitter <NUM> and a receiver <NUM> may be configured to transmit and/or receive time and/or frequency resource partitioning information. In some implementations, the transceiver <NUM> may be configured to transmit in different types of subframes and slots including, but not limited to, usable, non-usable and flexibly usable subframes and slot formats.

The node <NUM> may include a variety of computer-readable media. Computer-readable media can be any available media that can be accessed by the node <NUM> and include both volatile and non-volatile media, removable and non-removable media. By way of example, and not limitation, computer-readable media may comprise computer storage media and communication media. Computer storage media includes both volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data.

Computer storage media includes RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices. Computer storage media does not comprise a propagated data signal. Communication media typically embodies computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer-readable media.

The memory <NUM> may include computer-storage media in the form of volatile and/or non-volatile memory. The memory <NUM> may be removable, non-removable, or a combination thereof. Exemplary memory includes solid-state memory, hard drives, optical-disc drives, and etc. As illustrated in <FIG>, The memory <NUM> may store computer-readable, computer-executable instructions <NUM> (e.g., software codes) that are configured to, when executed, cause the processor <NUM> to perform various functions described herein, for example, with reference to <FIG>. Alternatively, the instructions <NUM> may not be directly executable by the processor <NUM> but be configured to cause the node <NUM> (e.g., when compiled and executed) to perform various functions described herein.

The processor <NUM> may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an ASIC, and etc. The processor <NUM> may include memory. The processor <NUM> may process the data <NUM> and the instructions <NUM> received from the memory <NUM>, and information through the transceiver <NUM>, the base band communications module, and/or the network communications module. The processor <NUM> may also process information to be sent to the transceiver <NUM> for transmission through the antenna <NUM>, to the network communications module for transmission to a core network.

Claim 1:
A method of random access resource selection, the method comprising:
transmitting (<NUM>), by a target Base Station, BS, a first Synchronization Signal Block, SSB, to a User Equipment, UE, the first SSB associated with a first contention-free random access resource for the UE to transmit a random access preamble;
transmitting (<NUM>), by the target BS, a second SSB to the UE, the second SSB associated with a contention-based random access resource; and
in a case that a first Synchronization Signal-Reference Signal Received Power, SS-RSRP, of the first SSB is not greater than an SS-RSRP threshold and a second SS-RSRP of the second SSB is greater than the SS-RSRP threshold, receiving (<NUM>), by the target BS, the random access preamble from the UE using the contention-based random access resource, wherein:
when dedicated Radio Resource Control, RRC, signaling, generated by the target BS, indicates the contention-based random access resource, the contention-based random access resource is determined based on the dedicated RRC signaling, and
when the dedicated RRC signaling does not indicate the contention-based random access resource, the contention-based random access resource is determined based on a common random access configuration broadcast by a source BS.