Methods and apparatus for enhanced beam reports and uplink synchronization for mobility procedures in wireless communication

Abstract

Methods and apparatus are provided for beam reporting and uplink synchronization. A UE is configured to support an uplink procedure that is after a cell switch command reception. Methods are also provided for differential encoding and handling PRACH overlap with uplink transmissions on a serving cell.

Description

METHODS AND APPARATUS FOR ENHANCED BEAM REPORTS AND UPLINKSYNCHRONIZATION FOR MOBILITY PROCEDURES IN WIRELESSCOMMUNICATIONTECHNICAL.FIELD

[0001] This application relates generally to wireless communication systems, including beam reporting and uplink synchronization.BACKGROUND

[0002] Wireless mobile communication technology uses various standards and protocols to transmit data between a base station and a wireless communication device. Wireless communication system standards and protocols can include, for example, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) (e.g., 4G), 3GPP New Radio (NR) (e.g., 5G), and Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard for Wireless Local Area Networks (WLAN) (commonly known to industry groups as Wi-Fi®).

[0003] As contemplated by the 3GPP, different wireless communication systems' standards and protocols can use various radio access networks (RANs) for communicating between a base station of the RAN (which may also sometimes be referred to generally as a RAN node, a network node, or simply a node) and a wireless communication device known as a user equipment (UE). 3GPP RANs can include, for example, Global System for Mobile communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE) RAN (GERAN), Universal Terrestrial Radio Access Network (UTRAN), Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and / or Next- Generation Radio Access Network (NG-RAN).

[0004] Each RAN may use one or more radio access technologies (RATs) to perform communication between the base station and the UE. For example, the GERAN implements GSM and / or EDGE RAT, the UTRAN implements Universal Mobile Telecommunication System (UMTS) RAT or other 3GPP RAT, the E-UTRAN implements LTE RAT (sometimes simply referred to as LTE), and NG-RAN implements NR RAT (sometimes referred to herein as 5G RAT, 5GNR RAT, or simply NR). In certain deployments, the E-UTRAN may also implement NR RAT. In certain deployments, NG-RAN may also implement LTE RAT.

[0005] A base station used by a RAN may correspond to that RAN. One example of an E-UTRAN base station is an Evolved Universal Terrestrial Radio Access Network (E- UTRAN) Node B (also commonly denoted as evolved Node B, enhanced Node B, eNodeB, or eNB). One example of an NG-RAN base station is a next generation Node B (also sometimes referred to as a g Node B or gNB).

[0006] A RAN provides its communication services with external entities through its connection to a core network (CN). For example, E-UTRAN may utilize an Evolved Packet Core (EPC) while NG-RAN may utilize a 5G Core Network (5GC).

[0007] Frequency bands for 5G NR may be separated into two or more different frequency ranges. For example, Frequency Range 1 (FR1) may include frequency bands operating in sub-6 gigahertz (GHz) frequencies, some of which are bands that may be used by previous standards, and may potentially be extended to cover new spectrum offerings from 410 megahertz (MHz) to 7125 MHz. Frequency Range 2 (FR2) may include frequency bands from 24.25 GHz to 52.6 GHz. Note that in some systems, FR2 may also include frequency bands from 52.6 GHz to 71 GHz (or beyond). Bands in the millimeter wave (mmWave) range of FR2 may have smaller coverage but potentially higher available bandwidth than bands in FR1. Skilled persons will recognize these frequency ranges, which are provided by way of example, may change from time to time or from region to region.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0009] FIG. 1 illustrates a triggering CFRA procedure by a CSC MAC-CE for candidate cells, according to one embodiment.

[0010] FIG. 2 illustrates a flowchart of a method for a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein.

[0011] FIG. 3 illustrates a flowchart of a method for a base station in a wireless network, according to certain embodiments herein.

[0012] FIG. 4 illustrates a CFRA resource selection process based on TCLstate information in a CSC MAC-CE, according to one embodiment.

[0013] FIG. 5 illustrates a flowchart of a method for a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein.

[0014] FIG. 6 illustrates a flowchart of a method for a base station in a wireless network, according to certain embodiments herein.

[0015] FIG. 7 illustrates a procedure for PRACH RO selection for LTM, according to certain embodiments.

[0016] FIG. 8 illustrates a flowchart of a method of a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein.

[0017] FIG. 9A illustrates an Ll-RSRP encoding scheme for candidate cell reporting, according to one embodiment.

[0018] FIG. 9B illustrates an Ll-RSRP encoding scheme for candidate cell reporting, according to another embodiment.

[0019] FIG. 10 illustrates PRACH overlapping with UL transmission on a serving cell that is addressed by embodiments herein.

[0020] FIG. 11 illustrates an example architecture of a wireless communication system, according to embodiments disclosed herein.

[0021] FIG. 12 illustrates a system for performing signaling between a wireless device and a network device, according to embodiments disclosed herein.

[0022] Various embodiments are described with regard to a UE. However, reference to a UE is merely provided for illustrative purposes. The example embodiments may be utilized with any electronic component that may establish a connection to a network and is configured with the hardware, software, and / or firmware to exchange information and data with the network. Therefore, the UE as described herein is used to represent any appropriate electronic component.

[0023] Mobile services that use low-latency and high reliability performance (e.g., ultra reliable low latency communications (URLLC)) are emerging. While the 5G standard has been designed to address these services from the start, it is useful for the evolution of 5G NR to continuously enhance the mobility robustness performance for these challenging scenarios. For example, NR mobility enhancements may include layer 1 (LI) enhancements for inter-cell beam management, including LI measurement and reporting, and beam indication.

[0024] In certain wireless networks, for beam selection for synchronization signal / physical broadcast channel block (SSB) based Ll-reference signal received power (RSRP) measurement report, radio resource configuration (RRC) signaling may be used to configure L candidate cells and M beams per cell in a channel state information (CSI) report, where L 6 (

[0001] ,2,3,4) and M 6 (1,2, 3, 4). Certain such networks support a physical downlink control channel (PDCCH)-order contention free random access (CFRA) procedure for timing advance (TA) acquisition before cell switch command reception. However, this may increase UE complexity due to handling of potential overlapping transmissions between a physical random access channel (PRACH) procedure towards a candidate cell and uplink (UL) transmissions on a serving cell. Thus, it is useful to support a PRACH procedure that is triggered after a cell-switch command to simplify UE implementation.

[0025] Certain wireless networks support SSB-based RSRP beam measurement report for candidate cells and each report may include reporting for L > 1 cell and M beams per cell. However, such networks have not defined the exact LI -RSRP reporting format for candidate cells.

[0026] Lower layer-triggered mobility' (LTM) may be used in wireless communication networks to facilitate seamless handover or movement of mobile devices between different network access points, base stations, or cells. This mobility management technique operates at the lower layers of the network protocol stack, specifically at the physical layer (e.g., LI) and data link layer (e.g., layer 2 (L2)), to provide uninterrupted connectivity during the transition from one cell or network coverage area to another. Thus, LTM may also be referred to as Ll / L2-triggered mobility'. LTM may use continuous monitoring of the signal strength, quality, and other performance parameters of candidate cells. When certain predefined criteria are met, such as a significant degradation in signal strength or quality, the UE may be triggered to initiate a handover process to switch its connection to a candidate cell with better conditions. By using LTM, the handover process can be initiated proactively and automatically, without significant involvement from the network infrastructure or user intervention. This may result in a seamless transition for the UE, maintaining a stable and consistent connection throughout its movement. LTM enables smooth roaming and mobility management within wireless networks, enhancing the user experience and supporting variousapplications such as streaming media, real-time communications, and location-based services.

[0027] An LTM UE in certain systems, however, may not support overlapped uplink transmissions towards a serving cell and a candidate cell. Thus, it would be useful to define handling a PRACH transmission towards the candidate cell and other UL transmissions on the serving cell, e.g., as PRACH, physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), sounding reference signal (SRS), etc.

[0028] Triggering CFRA for UL synchronization with candidate cells - TA field indicator.

[0029] According to certain embodiments disclosed herein, a variety of approaches may be used to support UL synchronization (sync) procedures that are not earlier than cell switch command (CSC) reception. In certain embodiments, the CSC is received in a media access control (MAC) control element (MAC-CE). Thus, the CSC may be referred to herein as a CSC MAC-CE.

[0030] FIG. 1 illustrates a triggering CFRA procedure 100 by a CSC MAC-CE for candidate cells, according to one embodiment. As shown, the CSC MAC-CE payload includes a 1 -bit TA field indicator field (TAFI field 102) and a 12-bit TA field 104. The TAFI field 102 indicates the usage of the TA field 104 in the same CSC MAC-CE. When the TAFI field 102 is set to a first value (e.g., “0”), the 12 bits of the TA field 104 indicate a TA value 106. The UE may use the TA value 106 to adjust UL timing for an UL transmission on the candidate cell and may not need to perform a separate PRACH procedure to complete an LTM process.

[0031] When the TAFI field 102 is set to a second value (e.g., “1”), a first six bits of the TA field 104 indicate an SSB index 108 and a second six bits of the 104 indicate a preamble index 110. The TAFI field 102 set to the second value triggers a PRACH procedure, such as a CFRA operation, wherein the UE uses the SSB index 108 and the preamble index 110 in a PRACH transmission to the candidate cell. The UE uses the PRACH procedure to obtain a TA value to use to adjust UL timing for an UL transmission on the candidate cell to complete an LTM process.

[0032] In certain embodiments, triggering CFRA in the CSC MAC-CE may be configurable by RRC signaling for candidate cells using LTM operation. If the CSCMAC-CE is not configured by RRC signaling, the TAFI field 102 is not present in the CSC MAC-CE and the UE assumes the 12-bit TA field 104 indicates the TA value 106.

[0033] FIG. 2 illustrates a flowchart of a method 200 for a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein. The method 200 includes receiving 202, from a base station, a CSC MAC-CE. The method 200 further includes, when the CSC MAC-CE includes TAFI field set to a first value, or when the CSC MAC-CE does not include the TAFI field, determining 204 a first TA value from a TA field of the CSC MAC-CE and using 206 the first TA value to adjust UL timing for an UL transmission on the candidate cell. On the other hand, when the CSC MAC-CE includes the TAFI field set to a second value, the method 200 further includes determining 208 an SSB index and a preamble index from the TA field of the CSC MAC-CE, using 210 the SSB index and the preamble index associated with the SSB index to perform a PRACH procedure with the candidate cell to obtain a second TA value, and using 212 the second TA value to adjust the UL timing for the UL transmission on the candidate cell.

[0034] In some embodiments of the method 200, the TAFI field includes a single bit, and the TA field includes 12 bits. In some such embodiments, when the TAFI field is set to the first value, or when the CSC MAC-CE does not include the TAFI field, the 12 bits of the TA field indicate the first TA value. In some embodiments, when the TAFI field is set to the second value, a first six bits of the 12 bits of the TA field indicate an SSB index value and a second 6 bits of the 12 bits of the TA field indicate field a preamble index value.

[0035] In some embodiments of the method 200, the candidate cell is configured with an LTM operation.

[0036] In some embodiments, the method 200 further includes receiving, from the base station, before receiving the CSC MAC-CE, a PDCCH order instructing the UE to perform the PRACH procedure.

[0037] In some embodiments of the method 200, the PRACH procedure comprises a CFRA procedure.

[0038] FIG. 3 illustrates a flowchart of a method 300 for a base station in a wireless network, according to certain embodiments herein. The method 300 includes configuring 302, for a UE, a CSC MAC-CE to include a TAFI field during an LTM operation by one or more candidate cells. In response to a measurement report from the UE, the method300 further includes determining 306 to perform the LTM operation for a candidate cell of the one or more candidate cells, and transmitting 308, to the UE, the CSC MAC-CE comprising the TAFI field to indicate whether a TA field of the CSC MAC-CE includes a TA value or an SSB index and a preamble index. The method 300 further includes receiving an LTM completion message from the UE.

[0039] In some embodiments of the method 300, configuring the CSC MAC-CE comprises transmitting, to the UE, an RRC signal comprising LTM configuration information. In some such embodiments, the TAFI field comprises a single bit, and the TA field comprises 12 bits. In certain such embodiments, when the TAFI field is set to a first value, the 12 bits of the TA field indicate the TA value. When the TAFI field is set to a second value, a first six bits of the 12 bits of the TA field indicate an SSB index value and a second 6 bits of the 12 bits of the TA field indicate a preamble index value.

[0040] In some embodiments, the method 300 further comprises transmitting, to the UE, before transmitting the CSC MAC-CE, a PDCCH order instructing the UE to perform a PRACH procedure. The PRACH procedure may comprise a CFRA procedure.

[0041] Triggering CFRA for UL synchronization with candidate cells - CFRA resource selection based on TCUstate.

[0042] In another embodiment for triggering CFRA for UL synchronization with a candidate cell, CFRA resource selection is based on transmission configuration indicator (TCI)-state information in a CSC MAC-CE. CFRA resource indication may include two steps. In a first step, a dedicated RRC signal may configure a set of random access channel (RACH) resource pairs. In particular, the dedicated RRC signal may configure an SSB resource list including a list of CFRA-SSB-Resources, where each CFRA-SSB- Resource includes an SSB index and a corresponding preamble index. The dedicated RRC signal may also include a PRACH mask index that may be applied for the SSB resources signaled in the SSB resource list. In a second step, the UE transmits the PRACH preamble corresponding to the preamble index that is associated with the SSB that is a quasi co-located (QCL) source reference signal (RS) of the TCI-state indicated by the same CSC MAC-CE.

[0043] For example, FIG. 4 illustrates a CFRA resource selection process based on TCI-state information in a CSC MAC-CE, according to one embodiment. In the illustrated example, the UE receives a RACH resource list 402 in an RRC signal at a first time. The RACH resource list 402 comprises an SSB resource list shown in a first table404, which includes three CFRA-SSB-Resources (1, 2, 3) with corresponding SSB indexes (SSB #1, SSB #3, SSB #4) and preamble indexes (Preamble #21, Preamble #6, Preamble #8). In this example, the UE is also configured with a TCI-state list, as shown in a second table 406, with TCI-state indexes (1, 2, 3) and corresponding QCL source RS #1 and QCL source RS#2 SSB indexes (SSB#1, SSB #3, SSB #4).

[0044] A CSC MAC-CE 408, received at the UE from a base station, indicates TCI- state 2. From the configured TCI-state list, as shown in the second table 406, the UE determines that TCI-state 2 corresponds to QCL source RS #1 and / or QCL source RS #2 with SSB #3. Accordingly, the UE determines from the SSB resource list, as shown in the first table 404, that SSB #3 corresponds to Preamble #6. The UE then uses Preamble #6 in a CFRA transmission 410 to perform a CFRA procedure to obtain the UL TA for synchronization with a candidate cell.

[0045] FIG. 5 illustrates a flowchart of a method 500 for a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein. The method 500 includes receiving 502, from a base station, an RRC signal including an SSB resource list. The method 500 further includes receiving 504, from the base station, a CSC MAC-CE indicating a TCI-state. The method 500 further includes determining 506 an SSB index, from a TCI-state list, of a corresponding SSB that is used as a QCL RS for the TCI-state indicated in the CSC MAC-CE. The method 500 further includes determining 508 a preamble index associated with the SSB index. The method 500 further includes performing 510, using the SSB index and the preamble index, to perform a PRACH procedure with the candidate cell to obtain a TA value. The method 500 further includes using 512 the TA value to adjust UL timing for an UL transmission on the candidate cell.

[0046] In some embodiments of the method 500, the SSB resource list includes a list of CFRA SSB resources, where each CFRA SSB resource comprises respective SSB indexes and respective associated preamble indexes. In certain such embodiments, the RRC signal further includes a PRACH mask index to apply to the preamble indexes of the CFRA SSB resources in the SSB resource list.

[0047] In some embodiments of the method 500, the candidate cell is configured with an LTM operation.

[0048] In some embodiments, the method 500 further includes receiving, from the base station, before receiving the CSC MAC-CE, a PDCCH order instructing the UE to perform the PRACH procedure.

[0049] In some embodiments of the method 500, the PRACH procedure comprises a CFRA procedure.

[0050] FIG. 6 illustrates a flowchart of a method 600 for a base station in a wireless network, according to certain embodiments herein. The method 600 includes transmitting 602, to a UE, an RRC signal including an SSB resource list. The method 600 further includes configuring 604 a TCI-state list, wherein a TCI-state in the TCI- state list is configured an SSB index for a corresponding SSB that is used as a QCL source RS. The method 600 further includes transmitting 606, to the UE, a MAC-CE indicating the TCI-state that is used by the UE to determine the SSB index and a corresponding preamble index associated with the SSB index based on the SSB resource list.

[0051] In some embodiments of the method 600, SSB resource list includes a list of CFRA SSB resources where each CFRA resource comprises respective SSB indexes and respective associated preamble indexes. In certain such embodiments, the RRC signal further includes a PRACH mask index to apply to the preamble indexes of the CFRA SSB resources in the SSB resource list.

[0052] In some embodiments, the method 600 further includes transmitting, to the UE, before transmitting the CSC MAC-CE, a PDCCH order instructing the UE to perform a PRACH procedure.

[0053] Triggering CFRA for UL synchronization with candidate cells - PRACH transmission deferral.

[0054] In another embodiment for triggering CFRA for UL synchronization with a candidate cell, the UE defers PRACH transmission until cell switch command reception. The UE is configured to transmit a PDCCH order PRACH in an earliest valid RACH occasion (RO) that meets both of the following two conditions. The first condition is that a time “Ngap” between a last symbol of the PDCCH order and a first symbol of a PRACH transmission is larger or equal to a predetermined time period D. The second condition is that the first symbol of the PRACH transmission is later than a last received symbol of a physical downlink shared channel (PDSCH) transmission comprising the CSC MAC-CE.

[0055] For the first condition, the predetermined time period may be in terms of a number of symbols. In certain embodiments, the predetermined time period of the first condition is given by NT + Anwpswitching + Aoeiay, where parameter NT represents the PUSCH preparation time, parameter ABWPSwitching accounts for the activate UL bandwidth part (BWP) change (if the change happens), and the parameter Aoeiay is 0.5 milliseconds (ms) for FR1 and 0.25 ms for FR2.

[0056] Skilled persons will recognize from the disclosure herein that the PUSCH preparation time may depend on a capability of the UE and a subcarrier spacing (SCS) of the downlink (DL) with which the physical downlink control channel (PDCCH) carrying the downlink control information (DCI) scheduling the PUSCH was transmitted and / or the uplink channel with which the PUSCH is to be transmitted. For example, 3GPP Technical Specification (TS) 38.214 defines a UE PUSCH preparation time based on a value / / in Table 6.4-1 for a first UE processing capability (capability 1) and in Table 6.4-2 for a second UE processing capability (capability 2). In certain embodiments herein, for the parameter NT, the PUSCH preparation time is based on UE processing capability 1 assuming a value / / corresponding to a smallest SCS between the PDCCH order and the PRACH transmission.

[0057] In certain embodiments, if there is no PDCCH order triggering CFRA that is received before the cell-switching command, the UE performs a contention-based RACH procedure (CBRA) to obtain the TA of the candidate cell.

[0058] By way of example, FIG. 7 illustrates a procedure for PRACH RO selection for LTM, according to certain embodiments. In particular, FIG. 7 shows, in the time domain, a PDCCH order 702 and a CSC MAC-CE 704 in DL with respect to a first PRACH RO 706, a second PRACH RO 708, a third PRACH RO 710, and a fourth PRACH RO 712 in UL.

[0059] In this example, it is assumed that the first PRACH RO 706 meets the first condition but not the second condition. In other words, Ngap > D = NT + Anwpswitchmg + Aoeiay, but the first symbol of the PRACH is not later than the last symbol of the PDSCH reception corresponding to the CSC MAC-CE 704. Thus, the UE does not select the first PRACH RO 706. Instead, in response to the PDCCH order 702, the UE selects the second PRACH RO 708, which corresponds to the earliest RACH RO to meet both the first condition and the second condition. The UE sends a PRACH transmission in thesecond PRACH RO 708 to initiate a CFRA procedure to obtain the TA of the candidate cell.

[0060] FIG. 8 illustrates a flowchart of a method 800 of a UE to perform UL synchronization with a candidate cell, according to certain embodiments herein. The method 800 includes receiving 802, from a base station, a PDCCH order to initiate a PRACH procedure. When the PDCCH order is received before a MAC-CE, the method 800 includes performing 804, to the candidate cell, a PRACH transmission for a CFRA procedure at an earliest RO that satisfies a first condition and a second condition. The first condition comprises a gap time between a last symbol of the PDCCH order and a first symbol of the PRACH transmission is larger or equal to a predetermined time period. The second condition comprises the first symbol of the PRACH transmission is later than a last received symbol of a PDSCH transmission comprising the CSC MAC- CE. When the PDCCH order is not received before the CSC MAC-CE, the method 800 includes performing 806 a CBRA procedure with the candidate cell.

[0061] In some embodiments of the method 800, the predetermined time period is given by NT + ABWPSwitching + Aoeiay, where NT represents a PUS CH preparation time based on a processing capability of the UE, ABWPSwitching accounts for any UL BWP switching time, and Aoeiay is a delay time based on a frequency range. In certain such embodiments, the PUSCH preparation time assumes a smallest SCS between the PDCCH order and the PRACH transmission. In addition, or in other embodiments, the delay time, Aoeiay, is 0.5 ms for FR1 and 0.25 ms for FR2.

[0062] In some embodiments of the method 800, the candidate cell is configured with an LTM operation.

[0063] Ll-RSRP reporting for measured candidate cells.

[0064] According to certain embodiments disclosed herein, a variety of approaches may be used, when the number of reported candidate cells is larger than one, to reduce or minimize the reporting overhead. In one embodiment, for example, two-step differential encoding is used. In a first step, differential Ll-RSRP encoding is performed for each candidate cell, which results in one absolute Ll-RSRP value and M-l differential Ll- RSRP values for a single cell relative to the largest measured Ll-RSRP for the candidate cell. In a second step, the differential Ll-RSRP value is computed among the largest measured Ll-RSRPs for the reported candidate cells, which results in one absolute Ll- RSRP value and L differential Ll-RSRP values.

[0065] For example, FIG. 9A illustrates an Ll-RSRP encoding scheme for candidate cell reporting, according to one embodiment. This example assumes two candidate cells, where each candidate cell comprises M = 3 Ll-RSRP reports. In the first step (Step-1), differential encoding is performed for each candidate cell based on the largest Ll-RSRP for that cell. In the second step (Step-2), the largest RSRP across the two candidate cell is encoded using absolute value and the others are encoded using differential schemes. Note that the reference RSRPs are different for different Ll-RSRP in Step-1 and Step-2, as shown in FIG. 9A.

[0066] In another embodiment, the UE uses differential Ll-RSRP based reporting for each reported candidate cell. For example, the largest measured value of Ll-RSRP is quantized to a 7-bits value in the range of [-140, -44] decibel-milliwatt (dBm) with 1 decibel (dB) step size. For other beams of the same reported candidate cell, the measured value of Ll-RSRP is quantized to a 4-bits value with 2 dB step size with the reference to the largest measured LI - RSRP.

[0067] For example, FIG. 9B illustrates an Ll-RSRP encoding scheme for candidate cell reporting, according to another embodiment. Similar to the example shown in FIG. 9A, the example shown in FIG. 9B assumes two candidate cells, where each candidate cell comprises M = 3 Ll-RSRP reports. Differential encoding is performed for each candidate cell based on the largest Ll-RSRP for that cell. Unlike the example shown in FIG. 9A, there is no Step-2 in the example shown in FIG. 9B, and the largest RSRP of each candidate cell is encoded using absolute encoding.

[0068] PRACH overlapping with UL transmission on serving cell.

[0069] According to certain embodiments disclosed herein, a variety of approaches may be used to handle overlapping between PRACH transmission towards a candidate cell and UL transmission to serving cells. By way of example, FIG. 10 illustrates PRACH overlapping with UL transmission on a serving cell that is addressed by embodiments herein. In this example, a UE 1002 transmits a PUSCH 1004 to a base station 1006 of a serving cell and a PRACH 1008 to a base station 1010 of a candidate cell. As shown in FIG. 10, in the frequency domain, the PUSCH 1004 at least partially overlaps with the PRACH 1008.

[0070] In one embodiment, the overlapping is avoided by a network (NW) scheduler (i.e., the UE 1002 does not expect the PRACH transmission is overlapped with UL transmissions on serving cells). For example, the network may apply this embodimentwhen the UE 1002 indicates not supporting overlapping transmissions. In such situations, if overlapping occurs, handling it is up to UE implementation.

[0071] In another embodiment, the UE 1002 prioritizes the PDCCH-ordered PRACH transmission. The transmission of PDCCH order PRACH is controlled by the network. Further, there is a long round-trip time for PRACH retransmission due to the coordination between a source distributed unit (DU) and a target DU over backhaul link. Accordingly, the prioritization allows the UE 1002 to drop the overlapped UL transmissions of serving cells.

[0072] In addition, or in another embodiment, a hard-encoded prioritization rule maybe predefined. In one such embodiment, a PDCCH-ordered PRACH transmission on the candidate cell has a same priority as the PRACH on PCell. In another embodiment, a PDCCH-ordered PRACH transmission on the candidate cell has a same priority as PUCCH / PUSCH transmission with hybrid automatic repeat request acknowledgement (HARQ-ACK) information. In yet another embodiment, a PDCCH-ordered PRACH transmission on the candidate cell has a same priority as PRACH transmission on the serving cell other than a primary cell (PCell). If overlapped transmission occurs on the same priority channels, it may be left to UE implementation or the serving cell is prioritized.

[0073] In another embodiment, a 1 -bit prioritization order indictor (POI) field may be added into a PDCCH-order DCI format by repurposing the reserved bits in DCI format l_0. The value “0” indicates to prioritize the PRACH on the PCell if the PRACH on the candidate cell is overlapped with PRACH on the PCell. The value “1” indicates to prioritize the PRACH on the candidate cell if it is overlapped with PRACH on the PCell. For other overlapped UL transmissions on the serving cell, the PRACH transmission on the candidate cell is prioritized. This embodiment may be used, for example, when the PRACH on the PCell is triggered for a beam recovery purpose and, therefore, should be prioritized to maintain the connection with the serving cell.

[0074] FIG. 11 illustrates an example architecture of a wireless communication system 1100, according to embodiments disclosed herein. The following description is provided for an example wireless communication system 1100 that operates in conjunction with the LTE system standards and / or 5G or NR system standards as provided by 3GPP technical specifications.

[0075] As shown by FIG. 11, the wireless communication system 1100 includes UE 1102 and UE 1104 (although any number of UEs may be used). In this example, the UE 1102 and the UE 1104 are illustrated as smartphones (e.g., handheld touchscreen mobile computing devices connectable to one or more cellular networks), but may also comprise any mobile or non-mobile computing device configured for wireless communication.

[0076] The UE 1102 and UE 1104 may be configured to communicatively couple with a RAN 1106. In embodiments, the RAN 1106 may be NG-RAN, E-UTRAN, etc. The UE 1102 and UE 1104 utilize connections (or channels) (shown as connection 1108 and connection 1110, respectively) with the RAN 1106, each of which comprises a physical communications interface. The RAN 1106 can include one or more base stations (such as base station 1112 and base station 1114) that enable the connection 1108 and connection 1110.

[0077] In this example, the connection 1108 and connection 1110 are air interfaces to enable such communicative coupling, and may be consistent with RAT(s) used by the RAN 1106, such as, for example, an LTE and / or NR.

[0078] In some embodiments, the UE 1102 and UE 1104 may also directly exchange communication data via a sidelink interface 1116. The UE 1104 is shown to be configured to access an access point (shown as AP 1118) via connection 1120. By way of example, the connection 1120 can comprise a local wireless connection, such as a connection consistent with any IEEE 802.11 protocol, wherein the AP 1118 may comprise a Wi-Fi® router. In this example, the AP 1118 may be connected to another network (for example, the Internet) without going through a CN 1124.

[0079] In embodiments, the UE 1102 and UE 1104 can be configured to communicate using orthogonal frequency division multiplexing (OFDM) communication signals with each other or with the base station 1112 and / or the base station 1114 over a multicarrier communication channel in accordance with various communication techniques, such as, but not limited to, an orthogonal frequency division multiple access (OFDMA) communication technique (e.g., for downlink communications) or a single carrier frequency division multiple access (SC-FDMA) communication technique (e.g., for uplink and ProSe or sidelink communications), although the scope of the embodiments is not limited in this respect. The OFDM signals can comprise a plurality of orthogonal subcarriers.

[0080] In some embodiments, all or parts of the base station 1112 or base station 1114 may be implemented as one or more software entities running on server computers as part of a virtual network. In addition, or in other embodiments, the base station 1112 or base station 1114 may be configured to communicate with one another via interface 1122. In embodiments where the wireless communication system 1100 is an LTE system (e.g., when the CN 1124 is an EPC), the interface 1122 may be an X2 interface. The X2 interface may be defined between two or more base stations (e.g., two or more eNBs and the like) that connect to an EPC, and / or between two eNBs connecting to the EPC. In embodiments where the wireless communication system 1100 is an NR system (e.g., when CN 1124 is a 5GC), the interface 1122 may be an Xn interface. The Xn interface is defined between two or more base stations (e.g., two or more gNBs and the like) that connect to 5GC, between a base station 1112 (e.g., a gNB) connecting to 5GC and an eNB, and / or between two eNBs connecting to 5GC (e.g., CN 1124).

[0081] The RAN 1106 is shown to be communicatively coupled to the CN 1124. The CN 1124 may comprise one or more network elements 1126, which are configured to offer various data and telecommunications services to customers / subscribers (e.g., users of UE 1102 and UE 1104) who are connected to the CN 1124 via the RAN 1106. The components of the CN 1124 may be implemented in one physical device or separate physical devices including components to read and execute instructions from a machine- readable or computer-readable medium (e.g., a non-transitory machine-readable storage medium).

[0082] In embodiments, the CN 1124 may be an EPC, and the RAN 1106 may be connected with the CN 1124 via an SI interface 1128. In embodiments, the SI interface 1128 may be split into two parts, an SI user plane (Sl-U) interface, which carries traffic data between the base station 1112 or base station 1114 and a serving gateway (S-GW), and the SI -MME interface, which is a signaling interface between the base station 1112 or base station 1114 and mobility management entities (MMEs).

[0083] In embodiments, the CN 1124 may be a 5GC, and the RAN 1106 may be connected with the CN 1124 via an NG interface 1128. In embodiments, the NG interface 1128 may be split into two parts, an NG user plane (NG-U) interface, which carries traffic data between the base station 1112 or base station 1114 and a user plane function (UPF), and the SI control plane (NG-C) interface, which is a signaling interfacebetween the base station 1112 or base station 1114 and access and mobility management functions (AMFs).

[0084] Generally, an application server 1130 may be an element offering applications that use internet protocol (IP) bearer resources with the CN 1124 (e.g., packet switched data services). The application server 1130 can also be configured to support one or more communication services (e.g., VoIP sessions, group communication sessions, etc.) for the UE 1102 and UE 1104 via the CN 1124. The application server 1130 may communicate with the CN 1124 through an IP communications interface 1132.

[0085] FIG. 12 illustrates a system 1200 for performing signaling 1234 between a wireless device 1202 and a network device 1218, according to embodiments disclosed herein. The system 1200 may be a portion of a wireless communications system as herein described. The wireless device 1202 may be, for example, a UE of a wireless communication system. The network device 1218 may be, for example, a base station (e.g., an eNB or a gNB) of a wireless communication system.

[0086] The wireless device 1202 may include one or more processor(s) 1204. The processor(s) 1204 may execute instructions such that various operations of the wireless device 1202 are performed, as described herein. The processor(s) 1204 may include one or more baseband processors implemented using, for example, a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein.

[0087] The wireless device 1202 may include a memory 1206. The memory 1206 may be a non-transitory computer-readable storage medium that stores instructions 1208 (which may include, for example, the instructions being executed by the processor(s) 1204). The instructions 1208 may also be referred to as program code or a computer program. The memory 1206 may also store data used by, and results computed by, the processor(s) 1204.

[0088] The wireless device 1202 may include one or more transceiver(s) 1210 that may include radio frequency (RF) transmitter circuitry and / or receiver circuitry that use the antenna(s) 1212 of the wireless device 1202 to facilitate signaling (e.g., the signaling 1234) to and / or from the wireless device 1202 with other devices (e.g., the network device 1218) according to corresponding RATs.

[0089] The wireless device 1202 may include one or more antenna(s) 1212 (e.g., one, two, four, or more). For embodiments with multiple antenna(s) 1212, the wireless device 1202 may leverage the spatial diversity of such multiple antenna(s) 1212 to send and / or receive multiple different data streams on the same time and frequency resources. This behavior may be referred to as, for example, multiple input multiple output (MIMO) behavior (referring to the multiple antennas used at each of a transmitting device and a receiving device that enable this aspect). MIMO transmissions by the wireless device 1202 may be accomplished according to precoding (or digital beamforming) that is applied at the wireless device 1202 that multiplexes the data streams across the antenna(s) 1212 according to known or assumed channel characteristics such that each data stream is received with an appropriate signal strength relative to other streams and at a desired location in the spatial domain (e.g., the location of a receiver associated with that data stream). Certain embodiments may use single user MIMO (SU-MIMO) methods (where the data streams are all directed to a single receiver) and / or multi user MIMO (MU-MIMO) methods (where individual data streams may be directed to individual (different) receivers in different locations in the spatial domain).

[0090] In certain embodiments having multiple antennas, the wireless device 1202 may implement analog beamforming techniques, whereby phases of the signals sent by the antenna(s) 1212 are relatively adjusted such that the (joint) transmission of the antenna(s) 1212 can be directed (this is sometimes referred to as beam steering).

[0091] The wireless device 1202 may include one or more interface(s) 1214. The interface(s) 1214 may be used to provide input to or output from the wireless device 1202. For example, a wireless device 1202 that is a UE may include interface(s) 1214 such as microphones, speakers, a touchscreen, buttons, and the like in order to allow for input and / or output to the UE by a user of the UE. Other interfaces of such a UE may be made up of transmitters, receivers, and other circuitry (e.g., other than the transceiver(s) 1210 / antenna(s) 1212 already described) that allow for communication between the UE and other devices and may operate according to known protocols (e.g., Wi-Fi®, Bluetooth®, and the like).

[0092] The wireless device 1202 may include a beam report and UL sync module 1216. The beam report and UL sync module 1216 may be implemented via hardware, software, or combinations thereof. For example, the beam report and UL sync module 1216 may be implemented as a processor, circuit, and / or instructions 1208 stored in the memory1206 and executed by the processor(s) 1204. In some examples, the beam report and UL sync module 1216 may be integrated within the processor(s) 1204 and / or the transceiver(s) 1210. For example, the beam report and UL sync module 1216 may be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the processor(s) 1204 or the transceiver(s) 1210.

[0093] The beam report and UL sync module 1216 may be used for various aspects of the present disclosure, for example, aspects of FIG. 1, FIG. 2, FIG. 4, FIG. 5, FIG. 7, FIG. 8, FIG. 9 A, FIG. 9B, and FIG. 10.

[0094] The network device 1218 may include one or more processor(s) 1220. The processor(s) 1220 may execute instructions such that various operations of the network device 1218 are performed, as described herein. The processor(s) 1220 may include one or more baseband processors implemented using, for example, a CPU, a DSP, an ASIC, a controller, an FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein.

[0095] The network device 1218 may include a memory 1222. The memory 1222 may be a non-transitory computer-readable storage medium that stores instructions 1224 (which may include, for example, the instructions being executed by the processor(s) 1220). The instructions 1224 may also be referred to as program code or a computer program. The memory 1222 may also store data used by, and results computed by, the processor(s) 1220.

[0096] The network device 1218 may include one or more transceiver(s) 1226 that may include RF transmitter circuitry and / or receiver circuitry that use the antenna(s) 1228 of the network device 1218 to facilitate signaling (e.g., the signaling 1234) to and / or from the network device 1218 with other devices (e.g., the wireless device 1202) according to corresponding RATs.

[0097] The network device 1218 may include one or more antenna(s) 1228 (e.g., one, two, four, or more). In embodiments having multiple antenna(s) 1228, the network device 1218 may perform MIMO, digital beamforming, analog beamforming, beam steering, etc., as has been described.

[0098] The network device 1218 may include one or more interface(s) 1230. The interface(s) 1230 may be used to provide input to or output from the network device 1218. For example, a network device 1218 that is a base station may include interface(s)1230 made up of transmitters, receivers, and other circuitry (e.g., other than the transceiver(s) 1226 / antenna(s) 1228 already described) that enables the base station to communicate with other equipment in a core network, and / or that enables the base station to communicate with external networks, computers, databases, and the like for purposes of operations, administration, and maintenance of the base station or other equipment operably connected thereto.

[0099] The network device 1218 may include a beam report and UL sync module 1232. The beam report and UL sync module 1232 may be implemented via hardware, software, or combinations thereof. For example, the beam report and UL sync module 1232 may be implemented as a processor, circuit, and / or instructions 1224 stored in the memory 1222 and executed by the processor(s) 1220. In some examples, the beam report and UL sync module 1232 may be integrated within the processor(s) 1220 and / or the transceiver(s) 1226. For example, the beam report and UL sync module 1232 may be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the processor(s) 1220 or the transceiver(s) 1226.

[0100] The beam report and UL sync module 1232 may be used for various aspects of the present disclosure, for example, aspects of FIG. 1, FIG. 3, FIG. 4, FIG. 6, FIG. 7, FIG. 9 A, FIG. 9B, and FIG. 10.

[0101] Embodiments contemplated herein include an apparatus comprising means to perform one or more elements of method 200, method 500, and / or method 800. This apparatus may be, for example, an apparatus of a UE (such as a wireless device 1202 that is a UE, as described herein).

[0102] Embodiments contemplated herein 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 method 200, method 500, and / or method 800. This non- transitory computer-readable media may be, for example, a memory of a UE (such as a memory 1206 of a wireless device 1202 that is a UE, as described herein).

[0103] Embodiments contemplated herein include an apparatus comprising logic, modules, or circuitry to perform one or more elements of method 200, method 500, and / or method 800. This apparatus may be, for example, an apparatus of a UE (such as a wireless device 1202 that is a UE, as described herein).

[0104] Embodiments contemplated herein 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 one or more elements of method 200, method 500, and / or method 800. This apparatus may be, for example, an apparatus of a UE (such as a wireless device 1202 that is a UE, as described herein).

[0105] Embodiments contemplated herein include a signal as described in or related to one or more elements of method 200, method 500, and / or method 800.

[0106] Embodiments contemplated herein include a computer program or computer program product comprising instructions, wherein execution of the program by a processor is to cause the processor to carry out one or more elements of method 200, method 500, and / or method 800. The processor may be a processor of a UE (such as a processor(s) 1204 of a wireless device 1202 that is a UE, as described herein). These instructions may be, for example, located in the processor and / or on a memory of the UE (such as a memory 1206 of a wireless device 1202 that is a UE, as described herein).

[0107] Embodiments contemplated herein include an apparatus comprising means to perform one or more elements of method 300 and / or method 600. This apparatus may be, for example, an apparatus of a base station (such as a network device 1218 that is a base station, as described herein).

[0108] Embodiments contemplated herein 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 method 300 and / or method 600. This non-transitory computer-readable media may be, for example, a memory of a base station (such as a memory 1222 of a network device 1218 that is a base station, as described herein).

[0109] Embodiments contemplated herein include an apparatus comprising logic, modules, or circuitry to perform one or more elements of method 300 and / or method 600. This apparatus may be, for example, an apparatus of a base station (such as a network device 1218 that is a base station, as described herein).

[0110] Embodiments contemplated herein 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 one or more elements of method 300 and / or method 600. This apparatus may be,for example, an apparatus of a base station (such as a network device 1218 that is a base station, as described herein).

[0111] Embodiments contemplated herein include a signal as described in or related to one or more elements of method 300 and / or method 600.

[0112] Embodiments contemplated herein include a computer program or computer program product comprising instructions, wherein execution of the program by a processing element is to cause the processing element to carry out one or more elements of method 300 and / or method 600. The processor may be a processor of a base station (such as a processor(s) 1220 of a network device 1218 that is a base station, as described herein). These instructions may be, for example, located in the processor and / or on a memory of the base station (such as a memory 1222 of a network device 1218 that is a base station, as described herein).

[0113] 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, and / or methods as set forth herein. For example, a baseband processor as described herein 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 herein. For another example, circuitry associated with a UE, base station, network element, etc. 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 herein.

[0114] Any of the above described embodiments may be combined with any other embodiment (or combination of embodiments), 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.

[0115] Embodiments and implementations of the systems and methods described herein may include various operations, which may be embodied in machine-executable instructions to be executed by a computer system. A computer system may include one or more general-purpose or special-purpose computers (or other electronic devices). The computer system may include hardware components that include specific logic forperforming the operations or may include a combination of hardware, software, and / or firmware.

[0116] It should be recognized that the systems described herein include descriptions of specific embodiments. These embodiments can be combined into single systems, partially combined into other systems, split into multiple systems or divided or combined in other ways. In addition, it is contemplated that parameters, attributes, aspects, etc. of one embodiment can be used in another embodiment. The parameters, attributes, aspects, etc. are merely described in one or more embodiments for clarity, and it is recognized that the parameters, attributes, aspects, etc. can be combined with or substituted for parameters, attributes, aspects, etc. of another embodiment unless specifically disclaimed herein.

[0117] 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.

[0118] Although the foregoing has been described in some detail for purposes of clarity, it will be apparent that certain changes and modifications may be made without departing from the principles thereof. It should be noted that there are many alternative ways of implementing both the processes and apparatuses described herein. Accordingly, the present embodiments are to be considered illustrative and not restrictive, and the description is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

Claims

1. A method for a user equipment (UE) to perform uplink (UL) synchronization with a candidate cell, the method comprising: receiving, from a base station, a cell switch command (CSC) media access control (MAC) control element (MAC-CE); when the CSC MAC-CE includes a timing advance (TA) field indicator (TAFI) field set to a first value, or when the CSC MAC-CE does not include the TAFI field: determining a first TA value from a TA field of the CSC MAC-CE; and using the first TA value to adjust UL timing for an UL transmission on the candidate cell; and when the CSC MAC-CE includes the TAFI field set to a second value: determining a synchronization signal / physical broadcast channel block (SSB) index and a preamble index from the TA field of the CSC MAC-CE; using the SSB index and the preamble index associated with the SSB index to perform a physical random access channel (PRACH) procedure with the candidate cell to obtain a second TA value; and using the second TA value to adjust the UL timing for the UL transmission on the candidate cell.

2. The method of claim 1, wherein the TAFI field comprises a single bit, and wherein the TA field comprises 12 bits.

3. The method of claim 2, wherein when the TAFI field is set to the first value, or when the CSC MAC-CE does not include the TAFI field, the 12 bits of the TA field indicate the first TA value, and wherein when the TAFI field is set to the second value, a first six bits of the 12 bits of the TA field indicate an SSB index value and a second 6 bits of the 12 bits of the TA field indicate a preamble index value.

4. The method of claim 1, wherein the candidate cell is configured with a lower layer- triggered mobility (LTM) operation.

5. The method of claim 1, further comprising receiving, from the base station, before receiving the CSC MAC-CE, a physical downlink control channel (PDCCH) order instructing the UE to perform the PRACH procedure.

6. The method of claim 1, wherein the PRACH procedure comprises a contention free random access (CFRA) procedure.

7. A method for a base station in a wireless network, the method comprising: configuring, for a user equipment (UE), a cell switch command (CSC) media access control (MAC) control element (MAC-CE) to include, during a lower layer- triggered mobility (LTM) operation by one or more candidate cells, a timing advance (TA) field indicator (TAFI) field; in response to a measurement report from the UE: determining to perform the LTM operation for a candidate cell of the one or more candidate cells; and transmitting, to the UE, the CSC MAC-CE comprising the TAFI field to indicate whether a TA field of the CSC MAC-CE includes: a TA value; or a synchronization signal / physical broadcast channel block (SSB) index and a preamble index; and receiving, from the UE, an LTM completion message.

8. The method of claim 7, wherein configuring the CSC MAC-CE comprises transmitting, to the UE, a radio resource control (RRC) signal comprising LTM configuration information.

9. The method of claim 7, wherein the TAFI field comprises a single bit, and wherein the TA field comprises 12 bits.

10. The method of claim 9, wherein when the TAFI field is set to a first value, the 12 bits of the TA field indicate the TA value, and wherein when the TAFI field is set to a second value, a first six bits of the 12 bits of the TA field indicate an SSB index value and a second 6 bits of the 12 bits of the TA field indicate a preamble index value.

11. The method of claim 7, further comprising transmitting, to the UE, before transmitting the CSC MAC-CE, a physical downlink control channel (PDCCH) order instructing the UE to perform a physical random access channel (PRACH) procedure.

12. The method of claim 11, wherein the PRACH procedure comprises a contention free random access (CFRA) procedure.

13. A method for a user equipment (UE) to perform uplink (UL) synchronization with a candidate cell, the method comprising: receiving, from a base station, a radio resource control (RRC) signal comprising a synchronization signal / physical broadcast channel block (SSB) resource list; receiving, from the base station, a cell switch command (CSC) media access control (MAC) control element (MAC-CE) indicating a transmission configuration indicator (TCI)-state; determining an SSB index, from a TCI-state list, of a corresponding SSB that is used as a quasi co-located (QCL) source reference signal (RS) for the TCI-state indicated in the CSC MAC-CE; determining a preamble index associated with the SSB index; performing, using the SSB index and the preamble index, to perform a physical random access channel (PRACH) procedure with the candidate cell to obtain a timing advance (TA) value; and using the TA value to adjust UL timing for an UL transmission on the candidate cell.

14. The method of claim 13, wherein the SSB resource list comprises a list of contention free random access (CFRA) SSB resources, where each CFRA SSB resource comprises respective SSB indexes and respective associated preamble indexes.

15. The method of claim 14, wherein the RRC signal further comprises a PRACH mask index to apply to the preamble indexes of the CFRA SSB resources in the SSB resource list.

16. The method of claim 13, wherein the candidate cell is configured with a lower layer- triggered mobility (LTM) operation.

17. The method of claim 13, further comprising receiving, from the base station, before receiving the CSC MAC-CE, a physical downlink control channel (PDCCH) order instructing the UE to perform the PRACH procedure.

18. The method of claim 13, wherein the PRACH procedure comprises a contention free random access (CFRA) procedure.

19. A method for a base station in a wireless network, the method comprising:transmitting, to a user equipment (UE), a radio resource control (RRC) signal comprising a synchronization signal / physical broadcast channel block (SSB) resource list; configuring a transmission configuration indicator (TCI)-state list, wherein a TCI-state in the TCI-state list is configured an SSB index for a corresponding SSB that is used as a quasi co-located (QCL) source reference signal (RS); and transmitting, to the UE, a cell switch command (CSC) media access control (MAC) control element (MAC-CE) indicating the TCI-state that is used by the UE to determine the SSB index and a corresponding preamble index associated with the SSB index based on the SSB resource list.

20. The method of claim 19, wherein the SSB resource list comprises a list of contention free random access (CFRA) SSB resources where each CFRA SSB resource comprises respective SSB indexes and respective associated preamble indexes.

21. The method of claim 20, wherein the RRC signal further comprises a physical random access channel (PRACH) mask index to apply to the preamble indexes of the CFRA SSB resources in the SSB resource list.

22. The method of claim 19, further comprising transmitting, to the UE, before transmitting the CSC MAC-CE, a physical downlink control channel (PDCCH) order instructing the UE to perform a physical random access channel (PRACH) procedure.

23. A method for a user equipment (UE) to perform uplink (UL) synchronization with a candidate cell, the method comprising: receiving, from a base station, a physical downlink control channel (PDCCH) order to initiate a physical random access channel (PRACH) procedure; when the PDCCH order is received before a cell switch command (CSC) media access control (MAC) control element (MAC-CE): performing, to the candidate cell, a PRACH transmission for a contention free random access (CFRA) procedure at an earliest RACH occasion (RO) that satisfies a first condition and a second condition, wherein the first condition comprises a gap time between a last symbol of the PDCCH order and a first symbol of the PRACH transmission is larger or equal to a predetermined time period, andwherein the second condition comprises the first symbol of the PRACH transmission is later than a last received symbol of a physical downlink shared channel (PDSCH) transmission comprising the CSC MAC-CE; and when the PDCCH order is not received before the CSC MAC-CE, performing a contention-based RACH (CBRA) procedure with the candidate cell.

24. The method of claim 23, wherein the predetermined time period is given by NT + ABWPSwitching + Aoeiay, where NT represents a physical uplink shared channel (PUSCH) preparation time based on a processing capability of the UE, ABWPSwitching accounts for any UL bandwidth part (BWP) switching time, and Aoeiay is a delay time based on a frequency range.

25. The method of claim 24, wherein the PUSCH preparation time assumes a smallest subcarrier spacing (SCS) between the PDCCH order and the PRACH transmission.

26. The method of claim 24, wherein the delay time, Aoeiay, is 0.5 milliseconds (ms) for a first frequency range (FR1) and 0.25 ms for a second frequency range (FR2).

27. The method of claim 23, wherein the candidate cell is configured with a lower layer- triggered mobility (LTM) operation.

28. An apparatus comprising means to perform the method of any of claim 1 to claim 27.

29. A 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 the method of any of claim 1 to claim 27.

30. An apparatus comprising logic, modules, or circuitry to perform the method of any of claim 1 to claim 27.

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