Method and apparatus for handling timing advance of cell in wireless communication system

Abstract

A method and apparatus for handling a timing advance for a cell in a wireless communication system are provided, including a user equipment receiving a configuration indicating at least one candidate cell including a first candidate cell, storing a first timing advance associated with the first candidate cell, and clearing or discarding a first timing advance associated with the first candidate cell in response to at least one of: expiration of a timer associated with the first timing advance; performing radio resource control reestablishment; the user equipment enters an RRCIDLE state or an RRCINACTIVE state; changing a serving cell; or when the list or set of stored timing advances for the at least one candidate cell is full, the user equipment stores a second timing advance.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 524,548, filed on June 30, 2023, and U.S. Provisional Patent Application No. 63 / 524,566, filed on June 30, 2023; each of the applications and publications cited therein are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates generally to wireless communication networks, and more particularly, to methods and apparatus for handling timing advance of cells in a wireless communication system. Background Art

[0004] With the rapid growth of the demand for transmitting large amounts of data to and from mobile communication devices, traditional mobile voice communication networks have evolved into networks that communicate using Internet Protocol (IP) packets. This IP packet communication can provide IP-bearing voice, multimedia, multicast and on-demand communication services for users of mobile communication devices.

[0005] An exemplary network structure is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system can provide high data throughput to enable the above-mentioned IP-bearing voice and multimedia services. Currently, the 3GPP standards organization is discussing new next-generation (e.g., 5G) radio technologies. Therefore, changes to the current body of 3GPP standards are currently being submitted and considered to enable the 3GPP standards to evolve and complete. Summary of the invention

[0006] A method, system and apparatus are provided for handling timing advance for cells in a wireless communication system by obtaining and storing timing advance for candidate cells before L1 / L2 triggered mobility.

[0007] In various embodiments, a method for a user equipment (UE) in a wireless communication system includes receiving a configuration indicating at least one candidate cell including a first candidate cell, storing a first TA associated with the first candidate cell, and clearing or discarding the first TA associated with the first candidate cell in response to at least one of the following: expiration of a timer associated with the first TA; performing radio resource control (RRC) re-establishment; the UE entering an RRC_IDLE state or an RRC_INACTIVE state; a serving cell change; and / or the UE storing a second TA when a list or set of stored TAs for the at least one candidate cell is full.

[0008] In various embodiments, a method of a UE in a wireless communication system includes receiving a configuration indicating at least one candidate cell including a first candidate cell, storing a first TA associated with the first candidate cell, and transmitting a report to a network, wherein the report indicates information related to the first TA. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A diagram showing a wireless communication system according to an embodiment of the present invention.

[0010] Figure 2 is a block diagram of a transmitter system (also referred to as an access network) and a receiver system (also referred to as a user equipment or UE) according to an embodiment of the present invention.

[0011] Figure 3 is a functional block diagram of a communication system according to an embodiment of the present invention.

[0012] Figure 4 According to an embodiment of the present invention Figure 3 Functional block diagram of the program code.

[0013] Figure 5 It is from 3GPP 38.321.v17.2.0 Figure 6 .1.3.4-1: Reappearance of the Timing Advance Command MAC CE.

[0014] Figure 6 It is from 3GPP 38.321v17.2.0 Figure 6 .1.3.4a-1: Reappearance of Absolute Timing Advance Command MAC CE. Figure 7 It is from 3GPP 38.331v17.2.0 Figure 5 .3.7.1-1: Reappearance of successful RRC connection re-establishment.

[0015] Figure 8 It is from 3GPP 38.331v17.2.0 Figure 5.3.7.1-2: RRC re-establishment falls back to the re-establishment of successful RRC establishment.

[0016] Fig. 9 It is from 3GPP 38.331v17.2.0 Figure 5 .4.3.1-1: Successful reproduction of mobility from NR.

[0017] Fig.10 It is from 3GPP 38.331v17.2.0 Figure 5 .4.3.1-2: Reproduction of mobility failure from NR.

[0018] Fig.11 This is a reproduction of Figure x of the signalling procedures for LTM from R2-2213332 38.300 Operation CR introducing further mobility enhancements for NR.

[0019] Fig.12 It is from 3GPP 38.211v17.1.0 Figure 4 .3.1-1: Reproduction of uplink-downlink timing relationship. Fig.13 is a diagram of an example of a UE storing / maintaining a maximum number of stored TAs according to an embodiment of the present invention.

[0020] Fig.14 4 is an example diagram of a UE storing a maximum of three TAs, TA1, TA2 and TA3 for candidate cells 1, 2 and 3 respectively, according to an embodiment of the present invention.

[0021] Fig.15 4 is a diagram showing an example in which the UE stores TA1 for the candidate cell 1 and TA2 for the candidate cell 2 before timing t1 according to an embodiment of the present invention.

[0022] Fig.16 4 is a diagram showing an example in which the UE stores TA1 and TA2 for candidate cells 1 and 2 according to an embodiment of the present invention, where TA2 becomes invalid at timing t1.

[0023] Fig.17 is an example diagram according to an embodiment of the present invention, wherein at timing t0 , the UE reports to the NW a TA report indicating that the UE stores TA ( TA1 , TA2 ) for the candidate cell 1 .

[0024] Fig.18A is a diagram of an example of a report indicating one or more candidate configuration IDs associated with one or more candidate cells according to an embodiment of the present invention.

[0025] Fig.18Bis an example diagram of a report indicating a field / flag according to an embodiment of the present invention, wherein the field / flag indicates whether the report instructs the UE to add or clear the stored Ta for the indicated configured / associated candidate cell.

[0026] Fig.18C is a diagram of an example of a report indicating whether a report includes a TA value for each candidate cell reported according to an embodiment of the present invention.

[0027] Fig.19 is a flowchart of a method of a UE in a wireless communication system according to an embodiment of the present invention, the method including storing or maintaining a TA for a candidate cell and clearing the TA of the candidate cell in response to at least one of a possible event list.

[0028] Fig. 20 is a flow chart of a method of a UE in a wireless communication system according to an embodiment of the present invention, the method comprising transmitting a report to a network, wherein the report contains or indicates a TA storage status of one or more candidate cells.

[0029] Fig.21 It is a flowchart of a method of a UE in a wireless communication system according to an embodiment of the present invention, the method comprising receiving a configuration indicating at least one candidate cell including a first candidate cell, storing a first TA associated with the first candidate cell, and clearing or discarding the first TA associated with the first candidate cell in response to at least one in a list of possible events.

[0030] Fig. 22 is a flowchart of a method of a UE in a wireless communication system according to an embodiment of the present invention, the method comprising receiving a configuration indicating at least one candidate cell including a first candidate cell, storing a first TA associated with the first candidate cell, and transmitting a report to a network. DETAILED DESCRIPTION

[0031] The present invention described herein may be applied to or implemented in the exemplary wireless communication systems and devices described below. In addition, the present invention is mainly described in the context of the 3GPP architecture reference model. However, it should be understood that with the help of the disclosed information, those skilled in the art can easily adapt and use and implement aspects of the present invention in the 3GPP2 network architecture as well as other network architectures.

[0032] The exemplary wireless communication systems and devices described below employ wireless communication systems that support broadcast services. Wireless communication systems are widely deployed to provide various types of communications, such as voice, data, etc. These systems can be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), 3GPP Long Term Evolution (LTE) radio access, 3GPP Long Term Evolution Advanced (LTE-A) radio access, 3GPP2 Ultra Mobile Broadband (UMB), WiMax, 3GPP New Radio (NR), or some other modulation technology.

[0033] In particular, the exemplary wireless communication systems and devices described below may be designed to support one or more standards, such as those provided by a consortium named "3rd Generation Partnership Project" referred to herein as 3GPP, including: [1] 3GPP 38.321v17.2.0; [2] 3GPP 38.331v17.2.0; [3] RP-212710 New WID for NR Further Mobility Enhancement; [4] R2-2213332 38.300 Operational CR for Introducing NR Further Mobility Enhancement; [5] 3GPP RAN1#110b Report; [6] 3GPP RAN1#112 Report; [7] 3GPP RAN2#121bis Report; [8] 3GPP RAN2#122 Report; and [9] 3GPP 38.211v17.1.0. The standards and documents listed above are expressly and completely incorporated herein by reference in their entirety.

[0034] Figure 1 1 shows a multiple access wireless communication system according to an embodiment of the present invention. An access network 100 (AN) includes multiple antenna groups, one including 104 and 106, another including 108 and 110, and another including 112 and 114. Figure 11, only two antennas are shown for each antenna group, however, each antenna group may utilize more or fewer antennas. Access terminal (AT) 116 communicates with antennas 112 and 114, where antennas 112 and 114 transmit information to access terminal 116 via forward link 120 and receive information from AT 116 via reverse link 118. AT 122 communicates with antennas 106 and 108, where antennas 106 and 108 transmit information to AT 122 via forward link 126 and receive information from AT 122 via reverse link 124. In an FDD system, communication links 118, 120, 124, and 126 may use different frequencies for communication. For example, forward link 120 may use a different frequency than the frequency used by reverse link 118.

[0035] Each group of antennas and / or the area in which they are designed to communicate is often referred to as a sector of the access network. In an embodiment, the antenna groups are each designed to communicate with access terminals in a sector of the area covered by the access network 100.

[0036] In communicating via forward links 120 and 126, the transmit antennas of access network 100 utilize beamforming in order to improve the signal-to-noise ratio of the forward links for the different access terminals 116 and 122. Additionally, an access network that transmits to access terminals randomly dispersed throughout its coverage area using beamforming causes less interference to access terminals in neighboring cells than an access network that transmits to all of its access terminals via a single antenna.

[0037] AN may be a fixed station or base station for communicating with a terminal, and may also be referred to as an access point, Node B, base station, enhanced base station, eNodeB, or some other term. AT may also be referred to as user equipment (UE), a wireless communication device, a terminal, an access terminal, or some other term.

[0038] Figure 2 2 is a simplified block diagram of an embodiment of a transmitter system 210 (also referred to as an access network) and a receiver system 250 (also referred to as an access terminal (AT) or user equipment (UE)) in a MIMO system 200. At the transmitter system 210, traffic data for a number of data streams is provided from a data source 212 to a transmit (TX) data processor 214.

[0039] In one embodiment, each data stream is transmitted through a respective transmit antenna.TX data processor 214 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

[0040] The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream are then modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for the data stream to provide modulation symbols. Instructions executed by processor 230 may determine the data rate, coding, and modulation for each data stream. Memory 232 is coupled to processor 230.

[0041] The modulation symbols for all data streams are then provided to a TX MIMO processor 220, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor 220 then converts the N T The modulation symbol stream is provided to N T transmitters (TMTR) 222a through 222t. In certain embodiments, TX MIMO processor 220 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

[0042] Each transmitter 222 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (eg, amplifies, filters, and up-converts) the analog signals to provide a modulated signal suitable for transmission via a MIMO channel. T The antennas 224a to 224t transmit the N signals from the transmitters 222a to 222t. T a modulated signal.

[0043] At the receiver system 250, N R The transmitted modulated signals are received by each antenna 252a through 252r and the received signal from each antenna 252 is provided to a respective receiver (RCVR) 254a through 254r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.

[0044] RX data processor 260 then extracts the N R The receiver 254 receives and processes N R received symbol streams to provide N TThe RX data processor 260 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor 260 is complementary to the processing performed by the TX MIMO processor 220 and the TX data processor 214 at the transmitter system 210.

[0045] Processor 270 periodically determines which pre-coding matrix to use (discussed below). Processor 270 formulates a reverse link message comprising a matrix index portion and a rank value portion.

[0046] The reverse link message may include various types of information about the communication link and / or the received data stream. The reverse link message is then processed by the TX data processor 238 (which also receives traffic data for a number of data streams from the data source 236), modulated by the modulator 280, conditioned by the transmitters 254a to 254r, and transmitted back to the transmitter system 210.

[0047] At the transmitter system 210, the modulated signal from the receiver system 250 is received by the antenna 224, conditioned by the receiver 222, demodulated by the demodulator 240, and processed by the RX data processor 242 to extract the reverse link message transmitted by the receiver system 250. The processor 230 then determines which precoding matrix to use to determine the beamforming weights and then processes the extracted message.

[0048] The memory 232 may be used to temporarily store some buffer / calculated data from 240 or 242 via the processor 230, store some buffer data from 212, or store some specific program codes. Also, the memory 272 may be used to temporarily store some buffer / calculated data from 260 via the processor 270, store some buffer data from 236, or store some specific program codes.

[0049] Go to Figure 3 , this figure shows an alternative simplified functional block diagram of a communication device according to one embodiment of the present invention. Figure 3 As shown, the communication device 300 in the wireless communication system can be used to implement Figure 1UE (or AT) 116 and 122 in, and the wireless communication system is preferably an NR system. The communication device 300 may include an input device 302, an output device 304, a control circuit 306, a central processing unit (CPU) 308, a memory 310, a program code 312, and a transceiver 314. The control circuit 306 executes the program code 312 in the memory 310 through the CPU 308, thereby controlling the operation of the communication device 300. The communication device 300 can receive a signal input by a user through the input device 302 (e.g., a keyboard or a keypad), and can output images and sounds through the output device 304 (e.g., a monitor or a speaker). The transceiver 314 is used to receive and transmit wireless signals, pass the received signal to the control circuit 306, and wirelessly output the signal generated by the control circuit 306.

[0050] Figure 4 According to one embodiment of the present invention, Figure 3 4. In this embodiment, program code 312 includes application layer 400, layer 3 portion 402, and layer 2 portion 404, and is coupled to layer 1 portion 406. Layer 3 portion 402 typically performs radio resource control. Layer 2 portion 404 typically performs link control. Layer 1 portion 406 typically performs physical connectivity.

[0051] For LTE, LTE-A or NR systems, the layer 2 portion 404 may include a radio link control (RLC) layer and a medium access control (MAC) layer. The layer 3 portion 402 may include a radio resource control (RRC) layer.

[0052] Any two or more of the following paragraphs, (sub)bullets, points, actions or claims described in each invention may be logically, reasonably and appropriately combined to form a specific method.

[0053] Any sentence, paragraph, (sub) bullet, key point, action or claim described in each of the following invention paragraphs or sections can be implemented independently and individually to form a specific method or device. The following disclosure of the present invention, such as "based on", "more specifically", "example", etc., is only a possible embodiment that does not limit a specific method or device.

[0054] In 38.321 (e.g., [1] 3GPP 38.321 v17.2.0), the random access procedure, TA maintenance and random access procedure are introduced:

[0055] 5.2 Maintenance of uplink time alignment

[0056] RRC configures the following parameters to maintain UL time alignment:

[0057] - timeAlignmentTimer (per TAG), which controls how long the MAC entity considers the uplink time alignment of the serving cells belonging to the associated TAG;

[0058] - inactivePosSRS-TimeAlignmentTimer, which controls how long the MAC entity considers the positioning SRS transmission uplink time alignment in RRC_INACTIVE in clause 5.26;

[0059] -cg-SDT-TimeAlignmentTimer, which controls how long the MAC entity considers the uplink transmissions for CG-SDT to be uplink time aligned.

[0060] The MAC entity will:

[0061] 1> When a timing advance command MAC CE is received, and if N has been maintained with the indicated TAG TA (as defined in TS 38.211[8]), then:

[0062] 2> Apply timing advance command for the indicated TAG;

[0063] 2> If inactivePosSRS-TimeAlignmentTimer is configured and there is an ongoing positioning SRS transmission in RRC_INACTIVE as in clause 5.26:

[0064] 3> Start or restart the inactivePosSRS-TimeAlignmentTimer associated with the indicated TAG.

[0065] 2> If the CG-SDT procedure triggered as in clause 5.27 is in progress:

[0066] 3> Start or restart the cg-SDT-TimeAlignmentTimer associated with the indicated TAG.

[0067] 2> Otherwise:

[0068] 3> Start or restart the timeAlignmentTimer associated with the indicated TAG.

[0069] 1> When a timing advance command is received in a random access response message for a serving cell belonging to a TAG or in a MSGB for a SpCell:

[0070] 2> If the MAC entity does not select a random access preamble among the contention-based random access preambles:

[0071] 3> Apply timing advance command for this TAG;

[0072] 3> Start or restart the timeAlignmentTimer associated with this TAG.

[0073] 2> Otherwise, if the timeAlignmentTimer associated with this TAG is not running, then:

[0074] 3> Apply timing advance command for this TAG;

[0075] 3>Start the timeAlignmentTimer associated with this TAG;

[0076] 3> when contention resolution as described in clause 5.1.5 is deemed unsuccessful; or

[0077] 3> When contention resolution is deemed successful for the SI request as described in clause 5.1.5 after transmitting the HARQ feedback containing the UE contention resolution identity MAC CE for the MAC PDU:

[0078] 4> Stop the timeAlignmentTimer associated with this TAG.

[0079] 3> When contention resolution is deemed unsuccessful as described in clause 5.1.5:

[0080] 4> If the CG-SDT procedure triggered as in clause 5.27 is in progress:

[0081] 5>N TA The value is set to the value before applying the received timing advance command as in TS 38.211 [8].

[0082] 3> When contention resolution is considered successful for the random access procedure while the CG-SDT procedure is in progress:

[0083] 4> Stop the timeAlignmentTimer associated with this TAG;

[0084] 4> Start or restart the cg-SDT-TimeAlignmentTimer associated with this TAG.

[0085] 3> When contention resolution is considered successful for the random access procedure while SRS transmission in RRC_INACTIVE is in progress:

[0086] 4> Start or restart the inactivePosSRS-TimeAlignmentTimer associated with this TAG.

[0087] 2> Otherwise:

[0088] 3> Ignore the received timing advance command.

[0089] 1> When an Absolute Timing Advance Command is received in response to an MSGA transmission containing a C-RNTI MAC CE as specified in clause 5.1.4a:

[0090] 2> Apply timing advance command for PTAG;

[0091] 2> If the CG-SDT procedure is in progress:

[0092] 3> Start or restart the cg-SDT-TimeAlignmentTimer associated with PTAG.

[0093] 2> Otherwise:

[0094] 3> Start or restart the timeAlignmentTimer associated with PTAG.

[0095] 1> When receiving an indication from the upper layer to stop the inactivePosSRS-TimeAlignmentTimer:

[0096] 2>Stop inactivePosSRS-TimeAlignmentTimer.

[0097] 1> When receiving an indication from the upper layer to start the inactivePosSRS-TimeAlignmentTimer:

[0098] 2>Start or restart the inactivePosSRS-TimeAlignmentTimer.

[0099] 1> When the instruction to start cg-SDT-TimeAlignmentTimer has been received from the upper layer:

[0100] 2>Start cg-SDT-TimeAlignmentTimer.

[0101] 1> When an instruction to stop cg-SDT-TimeAlignmentTimer has been received from the upper layer:

[0102] 2> cg-SDT-TimeAlignmentTimer is considered expired.

[0103] 1> When an instruction to start the TimeAlignmentTimer associated with PTAG has been received from the upper layer:

[0104] 2>Start the TimeAlignmentTimer associated with PTAG.

[0105] 1>When timeAlignmentTimer expires:

[0106] 2> If timeAlignmentTimer is associated with PTAG:

[0107] 3> Clear all HARQ buffers for all serving cells;

[0108] 3> Notify RRC to release PUCCH for all serving cells, if configured;

[0109] 3> Notify RRC to release SRS for all serving cells, if configured;

[0110] 3> Clear any configured downlink assignments and configured uplink grants;

[0111] 3> Clear any PUSCH resources used for semi-persistent CSI reporting;

[0112] 3> All running timeAlignmentTimers are considered expired;

[0113] 3> Maintain N of all tags TA (defined in TS 38.211[8]).

[0114] 2> Otherwise, if timeAlignmentTimer is associated with a STAG, then all serving cells belong to this TAG:

[0115] 3> Clear all HARQ buffers;

[0116] 3> Notify RRC to release PUCCH, if configured;

[0117] 3> Notify RRC to release SRS, if configured;

[0118] 3> Clear any configured downlink assignments and configured uplink grants;

[0119] 3> Clear any PUSCH resources used for semi-persistent CSI reporting;

[0120] 3> Maintain the N of this TAG TA (defined in TS 38.211[8]).

[0121] 1>When inactivePosSRS-TimeAlignmentTimer expires:

[0122] 2> Notify RRC to release the positioning SRS configured for RRC_INACTIVE.

[0123] 1>When cg-SDT-TimeAlignmentTimer expires:

[0124] 2> Clear any configured uplink grants;

[0125] 2> If a PDCCH addressed to the C-RNTI of the MAC entity has not been received after the initial transmission of the CG-SDT with a CCCH message:

[0126] 3> The ongoing CG-SDT program will be deemed terminated;

[0127] 3> Indicate to the upper layer that the cg-SDT-TimeAlignmentTimer has expired.

[0128] 2> Clear all HARQ buffers;

[0129] 2> Maintain the N of this TAG TA (defined in TS 38.211[8]).

[0130] When the MAC entity stops uplink transmission due to the fact that the maximum uplink transmission timing difference between the TAGs of the MAC entity or the maximum uplink transmission timing difference between the TAGs of any MAC entity of the UE is exceeded, the MAC entity considers that the timeAlignmentTimer associated with the SCell is expired.

[0131] When the timeAlignmentTimer associated with the TAG to which the serving cell belongs is not running, the CG-SDT procedure is not in progress, or the SRS transmission in RRC_INACTIVE as in clause 5.26 is not in progress, the MAC entity shall not perform any uplink transmission on this serving cell except for the random access preamble and MSGA transmission. In addition, when the timeAlignmentTimer associated with the PTAG is not running, the CG-SDT procedure is not in progress, and the SRS transmission in RRC_INACTIVE as in clause 5.26 is not in progress, the MAC entity shall not perform any uplink transmission on any serving cell except for the random access preamble and MSGA transmission on the SpCell. The MAC entity shall not perform any uplink transmission except for the random access preamble and MSGA transmission when the cg-SDT-TimeAlignmentTimer is not running during the ongoing CG-SDT procedure triggered as in clause 5.27. The MAC entity shall not perform any uplink transmission except Random Access Preamble and MSGA transmission when the inactivePosSRS-TimeAlignmentTimer is not running during the SRS transmission procedure in RRC_INACTIVE as in clause 5.26.

[0132] 6.1.3.4 Timing Advance Command MAC CE

[0133] The Timing Advance Command MAC CE is identified by a MAC subheader with an LCID as specified in Table 6.2.1-1.

[0134] It has a fixed size and consists of a single octet defined as follows ( Figure 6 .1.3.4-1):

[0135] -TAG ID: This field indicates the TAG ID of the addressed TAG. The TAG containing the SpCell has TAG ID 0. The length of the field is 2 bits;

[0136] - Timing Advance Command: This field indicates the index value T used to control the amount of timing adjustment that the MAC entity (as specified in TS 38.213 [6]) must apply. A (0, 1, 2, ..., 63). The length of the field is 6 bits.

[0137] Figure 5 It is from 3GPP 38.321.v17.2.0 Figure 6 .1.3.4-1: Reappearance of the Timing Advance Command MAC CE.

[0138] 6.1.3.4a Absolute Timing Advance Command MAC CE

[0139] The Absolute Timing Advance Command MAC CE is identified by a MAC subheader with an eLCID as specified in Table 6.2.1-1b.

[0140] It has a fixed size and consists of two octets defined as follows ( Figure 6 .1.3.4a-1):

[0141] - Timing Advance Command: This field indicates the index value TA used to control the amount of timing adjustment that the MAC entity must apply in TS 38.213 [6]. The size of the field is 12 bits;

[0142] -R: Reserved bit, set to 0.

[0143] Figure 6 It is from 3GPP 38.321v17.2.0 Figure 6 .1.3.4a-1: Reappearance of Absolute Timing Advance Command MAC CE.

[0144] 3.1 Definition

[0145] Primary cell: An MCG cell operating on a primary frequency, where the UE performs an initial connection establishment procedure or initiates a connection re-establishment procedure.

[0146] Primary SCG cell: For dual connectivity operation, the SCG cell to which the UE performs random access when performing reconfiguration with synchronization procedure.

[0147] Secondary cell: A cell that provides additional radio resources on top of special cells for UEs configured with CA.

[0148] Secondary Cell Group: For a UE configured with dual connectivity, a subset of serving cells including a PSCell and zero or more secondary cells.

[0149] Serving cell: For a UE in RRC_CONNECTED and not configured to use CA / DC, there is only one serving cell including the primary cell. For a UE in RRC_CONNECTED and configured to use CA / DC, the term 'serving cell' is used to refer to the set of cells including the special cell and all secondary cells.

[0150] Special cell: For dual connectivity operation, the term special cell refers to the PCell of the MCG or the PSCell of the SCG. In other cases, the term special cell refers to the PCell.

[0151] Timing Advance Group: A group of serving cells configured by RRC for cells with configured UL using the same timing reference cell and the same timing advance value. The timing advance group of the SpCell containing the MAC entity is called the Primary Timing Advance Group (PTAG), while the term Secondary Timing Advance Group (STAG) refers to other TAGs.

[0152] In 38.331 (e.g., [2] 3GPP 38.331v17.2.0), RRC reconfiguration, cell group and serving cell configuration are introduced, including TAG configuration:

[0153] 4.2.1 UE states and state transitions between RATs

[0154] When an RRC connection is established, the UE is in the RRC_CONNECTED state or the RRC_INACTIVE state. If this is not the case, i.e. no RRC connection is established, then the UE is in the RRC_IDLE state. The RRC state can be further characterized as follows:

[0155] …

[0156] 5.3.5.5 Cell Group Configuration

[0157] 5.3.5.5.1 General

[0158] The network configures the UE with a primary cell group (MCG) and zero or one secondary cell groups (SCGs). In (NG)EN-DC, the MCG is configured as specified in TS 36.331

[10] , and for NE-DC, the SCG is configured as specified in TS 36.331

[10] . The network provides the configuration parameters of the cell group in the CellGroupConfig IE.

[0159] The UE performs the following actions based on the received CellGroupConfig IE:

[0160] 1> If CellGroupConfig contains spCellConfig with reconfigurationWithSync:

[0161] 2>Perform reconfiguration with synchronization according to 5.3.5.5.2;

[0162] 2> Resume all suspended radio bearers except the SRB of the source cell group, resume SCG transmission of all radio bearers, resume BH RLC channels, and resume SCG transmission of BH RLC channels for IAB-MT (if suspended);

[0163] 1> If CellGroupConfig contains rlc-BearerToReleaseList:

[0164] 2> Perform RLC bearer release as specified in 5.3.5.5.3;

[0165] 1> If CellGroupConfig contains rlc-BearerToAddModList:

[0166] 2> Perform RLC bearer addition / modification as specified in 5.3.5.5.4;

[0167] 1> If CellGroupConfig contains mac-CellGroupConfig:

[0168] 2>Configure the MAC entity of this cell group as specified in 5.3.5.5.5;

[0169] 1> If CellGroupConfig contains sCellToReleaseList:

[0170] 2>Perform SCell release as specified in 5.3.5.5.8;

[0171] 1>If CellGroupConfig contains spCellConfig:

[0172] 2>Configure SpCell as specified in 5.3.5.5.7;

[0173] 1> If CellGroupConfig contains sCellToAddModList:

[0174] 2> Perform SCell addition / modification as specified in 5.3.5.5.9;

[0175] 1> If CellGroupConfig contains bh-RLC-ChannelToReleaseList:

[0176] 2> Perform BH RLC channel release as specified in 5.3.5.5.10;

[0177] 1> If CellGroupConfig contains bh-RLC-ChannelToAddModList:

[0178] 2> Perform BH RLC channel addition / modification as specified in 5.3.5.5.11;

[0179] 5.3.5.5.2 Reconfiguration with synchronization

[0180] The UE shall perform the following actions to perform reconfiguration with synchronization.

[0181] 1> If AS security is not activated, then the actions are performed after going to RRC_IDLE as specified in 5.3.11, and the release cause is "other", after which the procedure ends;

[0182] 1> If DAPS bearer is not configured:

[0183] 2> Stop the timer T310 corresponding to SpCell (if it is running);

[0184] 1> If this procedure is executed for MCG:

[0185] 2> If timer T316 is running;

[0186] 3> Stop timer T316;

[0187] 3> Clear the information contained in VarRLF-Report, if it exists;

[0188] 2>Resume MCG transmission (if paused).

[0189] 1> Stop the timer T312 for the corresponding SpCell (if it is running);

[0190] 1>Start timer T304 for the corresponding SpCell, where the timer value is set to t304, as included in reconfigurationWithSync;

[0191] 1> If frequencyInfoDL is included:

[0192] 2> Treat the target SpCell as the SpCell on the SSB frequency indicated by frequencyInfoDL, which has a physical cell identity indicated by physCellId;

[0193] 1> Otherwise:

[0194] 2> Treat the target SpCell as a SpCell on the SSB frequency of the source SpCell, which has a physical cell identity indicated by physCellId;

[0195] 1>Start DL synchronization with the target SpCell;

[0196] 1> Apply the specified BCCH configuration defined in 9.1.1.1 to the target SpCell;

[0197] 1> Get the MIB of the target SpCell, which is scheduled as specified in TS 38.213

[13] ;

[0198] NOTE 1: The UE shall perform reconfiguration with synchronization as soon as possible after receiving the RRC message triggering the reconfiguration with synchronization, which may be before acknowledging successful reception (HARQ and ARQ) of this message.

[0199] NOTE 2: If the UE already has the required timing information, or the timing information is not needed for random access, the UE may omit reading the MIB.

[0200] NOTE 2a: UEs with DAPS bearers do not monitor system information updates in the source PCell.

[0201] 1> If any DAPS bearer is configured:

[0202] 2> Create a MAC entity for the target cell group with the same configuration as the MAC entity for the source cell group;

[0203] 2> For each DAPS bearer:

[0204] 3> Establish one or more RLC entities for the target cell group, which have the same configuration as the entity for the source cell group;

[0205] 3> Establish a logical channel for the target cell group, which has the same configuration as the channel for the source cell group;

[0206] NOTE 2b: For understanding, if DAPS bearer is configured, then the UE needs to check if the field daps-Config is present in the RadioBearerConfig IE received in radioBearerConfig or radioBearerConfig2.

[0207] 2>For each SRB:

[0208] 3> Establish an RLC entity for the target cell group, which has the same configuration as the entity for the source cell group;

[0209] 3> Establish a logical channel for the target cell group, which has the same configuration as the channel for the source cell group;

[0210] 2>Suspend the SRB used for the source cell group;

[0211] Note 3: empty

[0212] 2> Apply the value of newUE-Identity as the C-RNTI in the target cell group;

[0213] 2>Configure the lower layer for the target SpCell according to the received spCellConfigCommon;

[0214] 2> If the received reconfigurationWithSync contains any additional fields not previously covered, then configure the lower layers for the target SpCell according to the additional fields.

[0215] 1> Otherwise:

[0216] 2> Reset the MAC entity of this cell group;

[0217] 2> The SCells of this cell group that are not included in the SCellToAddModList in the RRCReconfiguration message (if configured) are considered to be in the deactivated state;

[0218] 2> Apply the value of newUE-Identity as the C-RNTI for this cell group;

[0219] 2>Configure the lower layer according to the received spCellConfigCommon;

[0220] 2> If the received reconfigurationWithSync contains any additional fields not previously covered, then configure the lower layer according to the additional fields.

[0221] 5.3.5.5.8SCell Release

[0222] The UE shall:

[0223] 1> If the release is triggered by the reception of sCellToReleaseList:

[0224] 2> For each sCellIndex value contained in sCellToReleaseList:

[0225] 3> If the current UE configuration contains an SCell with the value sCellIndex:

[0226] 4>Release SCell.

[0227] 5.3.5.5.9SCell Addition / Modification

[0228] The UE shall:

[0229] 1> For each sCellIndex value contained in sCellToAddModList and not part of the current UE configuration (SCell addition):

[0230] 2> According to sCellConfigCommon and sCellConfigDedicated, add the SCell corresponding to sCellIndex;

[0231] 2> If sCellState is included:

[0232] 3>Configure the lower layers to treat the SCell as active;

[0233] 2> Otherwise:

[0234] 3>Configure the lower layers to consider the SCell to be in a deactivated state;

[0235] 2>For each measId in measIdList contained in VarMeasConfig:

[0236] 3> if the SCell is not applicable for the associated measurement; and

[0237] 3> If the relevant SCell is contained in the cellsTriggeredList defined in the VarMeasReportList for this measId:

[0238] 4> For this measId, remove the relevant SCell from cellsTriggeredList defined in VarMeasReportList;

[0239] 1> For each sCellIndex value contained in sCellToAddModList and part of the current UE configuration (SCell modification):

[0240] 2> Modify SCell configuration according to sCellConfigDedicated;

[0241] 2> If sCellToAddModList is received in an RRCReconfiguration message containing reconfigurationWithSync, or is received in an RRCResume message, or is received in an RRCReconfiguration message containing reconfigurationWithSync embedded in an RRCResume message, or embedded in an RRCReconfiguration message, or embedded in an E-UTRARRCConnectionReconfiguration message, or embedded in an E-UTRA RRCConnectionResume message:

[0242] 3> If sCellState is included:

[0243] 4>Configure the lower layers to treat the SCell as active;

[0244] 3> Otherwise:

[0245] 4>Configure the lower layers to consider the SCell to be in a deactivated state.

[0246] 5.3.7RRC Connection Reestablishment

[0247] 5.3.7.1 General

[0248] Figure 7 It is from 3GPP 38.331v17.2.0 Figure 5 .3.7.1-1: Reappearance of successful RRC connection re-establishment.

[0249] Figure 8 It is from 3GPP 38.331v17.2.0 Figure 5 .3.7.1-2: RRC re-establishment falls back to the re-establishment of successful RRC establishment.

[0250] The purpose of this procedure is to re-establish the RRC connection. A UE in RRC_CONNECTED for which AS security has been activated in case of SRB2 and at least one DRB / Multicast MRB setup or for which the IAB is SRB2 may initiate the procedure in order to continue the RRC connection. The connection re-establishment is successful if the network is able to find and verify a valid UE context, or if the UE context cannot be retrieved and the network responds with RRCSetup according to section 5.3.3.4.

[0251] …

[0252] 5.3.5.13 Conditional Reconfiguration

[0253] 5.3.5.13.1 General

[0254] The network configures one or more candidate target SpCells for the UE in a conditional reconfiguration. The UE evaluates the conditions of each configured candidate target SpCell. The UE applies the conditional reconfiguration associated with one of the target SpCells that satisfies the associated execution condition. The network provides configuration parameters for the target SpCell in the ConditionalReconfiguration IE.

[0255] …

[0256] 5.4.3 Mobility from NR

[0257] 5.4.3.1 General

[0258] Fig. 9 It is from 3GPP 38.331v17.2.0 Figure 5 .4.3.1-1: Successful reproduction of mobility from NR.

[0259] Fig.10 It is from 3GPP 38.331v17.2.0 Figure 5 .4.3.1-2: Reproduction of mobility failure from NR.

[0260] The purpose of this procedure is to move a UE in RRC_CONNECTED to a cell using other RATs, such as E-UTRA, UTRA-FDD. The mobility procedure from NR covers the following mobility types:

[0261] - Handover, i.e. the MobilityFromNRCommand message contains the radio resources already allocated for the UE in the target cell;

[0262] CellGroupConfig

[0263] The CellGroupConfig IE is used to configure a master cell group (MCG) or a secondary cell group (SCG). A cell group includes a MAC entity, a set of logical channels with an associated RLC entity, a primary cell (SpCell), and one or more secondary cells (SCells).

[0264] CellGroupConfig Information Element

[0265]

[0266]

[0267]

[0268]

[0269] When introducing FeMIMO in the RRC specification (e.g., [6] 3GPP RAN1#112 report), measurement objects and serving cell configuration for additional cells are introduced:

[0270] -ServingCellConfig

[0271] IE ServingCellConfig is used to configure (add or modify) the UE with a serving cell, which can be a SpCell or SCell of an MCG or SCG. The parameters in this document are mainly UE-specific, but some are also cell-specific (e.g., in an additionally configured bandwidth portion). Only SCell release and addition are used to support reconfiguration between PUCCH and PUCCH-free SCells.

[0272] ServingCellConfig Information Elements

[0273]

[0274]

[0275]

[0276]

[0277]

[0278]

[0279]

[0280]

[0281]

[0282]

[0283]

[0284]

[0285]

[0286]

[0287]

[0288]

[0289]

[0290]

[0291]

[0292]

[0293]

[0294] Note: In the gNB / SK eNB In case of a change in the derived AS security keys, if reconfigurationWithSync is not included in the masterCellGroup, the network releases all existing MCG RLC bearers associated with the radio bearers with keyToUse set to secondary. gNB / K eNB In case of a derived AS security key change, if reconfigurationWithSync is not included in secondaryCellGroup, the network releases all existing SCG RLC bearers associated with the radio bearers with keyToUse set to primary.

[0295] -RACH-ConfigGeneric

[0296] The IE RACH-ConfigGeneric is used to specify random access parameters both for regular random access and for beam failure recovery.

[0297] RACH-ConfigGeneric Information Element

[0298]

[0299]

[0300]

[0301]

[0302] In the new WID for further mobility enhancement of NR (for example, [3] RP-212710 New WID for further mobility enhancement of NR), the mobility enhancement goals of NR are discussed:

[0303] 3 reasons

[0304] When a UE passes from the coverage area of ​​one cell to another, at some point a serving cell change needs to be performed. Currently, serving cell changes are triggered by L3 measurements and are done by reconfiguration triggered by RRC signaling with synchronization for changes of PCell and PSCell, and added for SCell release when applicable, with a complete reset of L2 (and L1) in all cases, and involving more latency, more overhead and more disruption time compared to beam switching mobility. The goal of L1 / L2 mobility enhancements is to be able to do serving cell changes via L1 / L2 signaling with such low latency, low overhead and low disruption time.

[0305] In Rel-17 Conditional PSCell Change (CPC) / Conditional PSCell Change / Addition (CPAC), a CPC / CPAC configured UE must release the CPC / CPAC configuration when performing random access to the target PSCell. Therefore, without reconfiguration and reinitialization of CPC / CPAC from the network, the UE has no opportunity to perform subsequent CPC / CPAC, which will delay the cell change and increase signaling overhead, especially in the case of frequent SCG changes operating on FR2. Therefore, MR-DC with selective activation of cell groups is intended to allow subsequent CPC / CPAC after changing the SCG without reconfiguration and reinitialization of CPC / CPAC preparation from the network, which can reduce the signaling overhead and interruption time of CPC / CPAC.

[0306] Currently, it is not possible to configure CHO and MR-DC at the same time. This limits the usefulness of these two features when MR-DC is configured. If not done in Rel-17, Rel-18 should specify a mechanism for configuring CHO and MR-DC at the same time. However, this may not be sufficient because the radio link quality of the configured PSCell may not be good enough or may not be the best candidate PSCell when the UE accesses the target PCell. This will therefore affect the UE's throughput, and Rel-18 CHO+MRDC may consider CHO that includes a target MCG and multiple candidate SCGs for CPC / CPAC to further improve CHO performance.

[0307] 4 Objectives

[0308] 4.1 Objectives of the Core WI

[0309] The detailed objectives of this work item are:

[0310] ○ Specify mechanisms and procedures for L1 / L2 based inter-cell mobility to reduce mobility latency:

[0311] -Configure and maintain multiple candidate cells to allow rapid application of candidate cell configuration [RAN2, RAN3]

[0312] - Dynamic switching mechanism between candidate serving cells (including SpCell and SCell) for potential applicable scenarios based on L1 / L2 signaling [RAN2, RAN1]

[0313] - L1 enhancements, including inter-cell beam management, L1 measurement and reporting, beam indication, and handling of asynchronous scenarios for TA management [RAN1, RAN2]

[0314] - CU-DU interface signalling to support L1 / L2 mobility (if required) [RAN3]

[0315] NOTE 1: FR2 specific enhancements (if present) are not excluded.

[0316] NOTE 2: The L1 / L2 based inter-cell mobility procedure is applicable to the following scenarios:

[0317] ◆With a serving cell change within a CG from standalone, CA and NR-DC cases

[0318] ◆Situation within CU and between DUs within CU (applicable to standalone and CA)

[0319] ◆Both the same frequency and different frequency

[0320] ◆Both FR1 and FR2

[0321] ○ Mechanisms and procedures for specifying MR-DC for selective activation of cell groups via L3 enhancement:

[0322] - Allows subsequent CPC / CPAC after changing SCG without reconfiguring and re-initiating CPC / CPAC [RAN2, RAN3, RAN4]

[0323] - To be determined: whether the Rel-17 CPC / CPAC mechanism will be used as a baseline

[0324] - To be determined: whether to limit MR-DC to EN-DC and NR-DC

[0325] ○ If this cannot be done in Rel-17, then specify CHO [RAN3, RAN2] containing the target MCG and target SCG

[0326] ○ Specify CHO [RAN3, RAN2] containing target MCG and candidate SCG for CPC / CPAC

[0327] - CHO containing target MCG and target SCG used as baseline

[0328] In the 3GPP specification 38.300 Operation CR introducing further mobility enhancements for NR (e.g., [4] R2-2213332 38.300 Operation CR introducing further mobility enhancements for NR), L1 / L2 triggered mobility (LTM) is introduced:

[0329] 9.2.3.x L1 / L2 Triggered Mobility

[0330] 9.2.3.x.1 General

[0331] LTM is a procedure in which the gNB receives L1 measurement reports from the UE and based on them the gNB changes the serving cell of the UE via MAC CE. The gNB prepares one or more candidate cells and provides the candidate cell configurations to the UE via RRC messages. LTM cell switching is then triggered by the gNB selecting one of the candidate configurations as the target configuration for LTM. Candidate cell configurations can only be added, modified and released by the network via RRC signaling.

[0332] Editor's note: Whether some optimizations such as release should be applied later is for further study.

[0333] Editor's Note: Current options for configuring LTM candidate cells:

[0334] a. An RRCReconfiguration message for a candidate target cell

[0335] b. One CellGroupConfig IE for each candidate target cell

[0336] The following principles apply to LTM:

[0337] - The candidate cell configuration may be provided as a delta configuration on top of the reference configuration. The reference configuration is managed separately and the UE stores the reference configuration as a separate configuration.

[0338] - The user plane is continuous whenever possible (e.g., within a DU) without the need for reset to avoid data loss and additional delays in data recovery.

[0339] - Security is not updated in LTM.

[0340] - Subsequent LTM between candidates can be performed (ie, the UE does not release other candidate cell configurations after LTM triggering) without RRC reconfiguration.

[0341] LTM supports intra-gNB-DU and intra-gNB-CU inter-gNB-DU mobility. LTM also supports inter-frequency mobility, including mobility to an inter-frequency cell that is not the current serving cell. The following scenarios are supported:

[0342] - PCell change in non-CA scenario,

[0343] - PCell change in CA scenario without SCell change,

[0344] -PCell change and SCell change in CA scenario, including the following cases:

[0345] a) Target PCell / target SCell is not the current serving cell (CA to CA scenario with PCell change)

[0346] b) The target PCell is the current SCell

[0347] c) The target SCell is the current PCell.

[0348] - Dual connectivity scenarios, at least for PSCell change cases without MN participation, ie intra-SN.

[0349] Inter-cell beam management is also supported, but it is not considered a prerequisite for using LTM.

[0350] Editor's note: The design based on intra-DU and inter-DU L1 / L2 mobility should share as much commonality as possible. Which aspects need to be different is for further study.

[0351] Editor's note: Whether ASN.1 decoding and validity / compliance checking of the candidate cell configuration is performed after receiving it and whether this needs to be specified is for further study.

[0352] 9.2.3.x.2C Plane Disposal

[0353] The cell handover trigger information is delivered in a MAC CE containing at least a candidate configuration index. The cell specific, radio bearer and measurement configurations may be part of the LTM candidate cell configuration.

[0354] Editor's note: Whether the MAC CE can indicate the TCI status (or other beam information) to be activated for the target cell is for further study.

[0355] Editor's note: Whether it should be possible to perform SCell activation / deactivation (in SC cells associated with the candidate configuration) at the same time as LTM triggers MAC CE is for further study.

[0356] The UE may perform CBRA or CFRA at cell handover. If the UE does not need to acquire the TA of the target cell during cell handover, the UE may also skip the random access procedure. RACH resources for CFRA are provided in the RRC configuration.

[0357] Editor's Note: Whether CFRA resources can be provided via MAC CE is for further study.

[0358] The overall procedure of LTM is shown in Figure x below. Subsequent LTMs are completed by repeating the early synchronization, LTM execution, and LTM completion steps without releasing other candidates after each LTM is completed.

[0359] Fig.11 This is a reproduction of Figure x from R2-2213332 38.300 Operation CR introducing further mobility enhancements for NR. The signalling procedures for LTM are shown in Figure x.

[0360] The LTM procedure is as follows.

[0361] 1.UE sends a MeasurementReport message to the gNB. The gNB decides to use LTM and initiates LTM candidate preparation.

[0362] 2. The gNB transmits an RRCReconfiguration message containing the configuration of one or more LTM candidate target cells to the UE.

[0363] 3. The UE stores the configuration of the LTM candidate target cell and sends an RRCReconfigurationComplete message to the gNB.

[0364] 4. The UE may perform DL synchronization and TA acquisition of candidate target cells before receiving the LTM cell handover command.

[0365] Editor's note: Support DL synchronization of candidate cells before cell handover command, at least based on SSB. Necessary mechanisms are for further study.

[0366] Editor's note: At least based on PDCCH ordered RACH, support for TA acquisition of candidate cells before LTM cell handover command, where PDCCH command is only triggered by the source cell. The detailed mechanism is for further study.

[0367] 5. The UE performs L1 measurements on the configured LTM candidate target cells and transmits a lower layer measurement report to the gNB.

[0368] 6. The gNB decides to perform LTM cell handover to the target cell and transmits a MAC CE triggering LTM cell handover with a candidate configuration index of the target cell. The UE switches to the configuration of the LTM candidate target cell.

[0369] Editor's Note: How beam pointing is accomplished is for further study.

[0370] 7. If TA is not available, the UE performs a random access procedure towards the target cell.

[0371] 8. The UE indicates successful completion of the LTM cell handover towards the target cell.

[0372] An uplink signal or message after the UE has switched to the target cell is used to indicate the successful completion of the LTM cell handover.

[0373] 9.2.3.x.3U plane handling

[0374] In LTM, whether the UE performs a partial or full MAC reset, re-establishes RLC, and performs data recovery of PDCP during cell handover is explicitly controlled by the network.

[0375] Editor's Note: Regarding determining whether to reset L2: Two options on the table:

[0376] 1) The UE determines whether the handover is an intra-DU handover or an inter-DU handover, and follows different rules or configurations for the two cases to control whether to reset. The determination may be based on the configuration (e.g., DU ID, cell group id, etc.)

[0377] 2) The UE receives a command to reset or not reset via MAC CE.

[0378] Editor's note: Some of the reset content is subject to further research.

[0379] Editor's note: For UE processing, assume that the following (non-exhaustive) is performed after receiving the cell handover command:

[0380] 1.MAC / RLC reset (when configured)

[0381] 2.RF re-tuning (e.g., frequency switching required), baseband re-tuning

[0382] Editor's note: How the UE determines the BWP (for DL ​​and UL) to use after the execution of L1 / L2 inter-cell mobility is for further study.

[0383] In the 3GPP RAN1#110b-e meeting ([5] 3GPP RAN1#110b report), the following agreement was reached on obtaining the TA of candidate cells before LTM:

[0384] protocol

[0385] Candidate cell TA acquisition before receiving a cell handover command is supported in L1 / L2 based mobility.

[0386] • For further study: whether this can be applied to the candidate cell when the candidate cell is a deactivated SCell (if defined in RAN2).

[0387] From the GTW meeting on October 19th

[0388] protocol

[0389] Regarding the mechanism of obtaining the TA of the candidate cell, the following solutions can be further studied:

[0390] ●RACH-based solution

[0391] ○ For example, PDCCH ordered RACH, UE triggered RACH, higher layer triggered RACH from NW other than L3 HO cmd

[0392] ● RACH-free solution

[0393] ○ For example, SRS-based TA acquisition, Rx timing difference-based, RACH-free mechanism in LTE, UE-based TA measurement (including UE-based TA measurement where one of the TACs is from the serving cell)

[0394] protocol

[0395] For candidate cell TA acquisition before receiving a cell handover command, at least the following alternatives for associating TA / TAG with candidate cells are studied:

[0396] ●Alternative 1: implicitly associate TA / TAG with candidate cells, e.g.

[0397] ○The association between TA / TAG and TCI status can be configured

[0398] ●Alternative 2: Explicitly associate TA / TAG with candidate cells, e.g.

[0399] ○ Provide association as part of candidate cell configuration

[0400] ○ Provides the association between TA / TAG and SSB / TRS as part of candidate cell configuration

[0401] In the 3GPP RAN1#112 meeting (e.g., [6] 3GPP RAN1#112 report), the following agreement was reached regarding PDCCH ordered RACH of candidate cells:

[0402] protocol

[0403] For PDCCH ordered RACH of candidate cells, RAR reception can be configured / indicated

[0404] ● If RAR reception is not configured / indicated (no RAR)

[0405] ○The TA value of the candidate cell is indicated in the cell handover command

[0406] ○ For further study: Should the UE retransmit PRACH when RAR reception is not configured / indicated?

[0407] ○ For further study: How does the UE determine the transmission power of the subsequent PRACH triggered by the PDCCH command?

[0408] If reception of RAR is configured / indicated (with RAR), then the following is for further study

[0409] ○ Is the RAR received from the serving cell or the candidate cell?

[0410] ■If the RAR is received from a candidate cell, is the Type1-PDCCH CSS of the candidate cell configured for the UE?

[0411] ○RAR content

[0412] ●For further study: Signaling for whether to receive RAR configuration / indication

[0413] ●UE can report support combination of using RAR only and without RAR, where support for one preset scheme is the baseline UE method for LTM

[0414] ● Send LS to RAN2 and RAN3 to check the feasibility of this protocol

[0415] ●Note: The definition of candidate cells depends on RAN2

[0416] protocol

[0417] ● For PDCCH command-based RACH for TA measurement of candidate cells, traditional CBRA is not supported

[0418] protocol

[0419] Regarding whether the UE should initiate PRACH retransmission when reception of RAR is not configured / indicated, select one of the following alternatives.

[0420] ● Alternative 1: Do not allow UE autonomous retransmissions of PRACH (e.g., by setting the number of allowed PRACH transmissions to PreambleTransMax=1 minimum)

[0421] ●Alternative 2: Allow UE autonomous retransmission of PRACH,

[0422] ○ The number of PRACH transmissions will be defined, for example, the number of RACH transmissions will be set to the minimum value of PreambleTransMax

[0423] protocol

[0424] If reception of a RAR is configured / indicated, the RAR contains at least the TA of the candidate cell.

[0425] The maximum number of TA values ​​that a UE can store is the UE's capability

[0426] ● To be further studied: whether RAR contains other parameters such as UE ID, candidate cell ID, etc.

[0427] protocol

[0428] Whether to receive RAR is configured by RRC.

[0429] In the RAN2#121bis meeting (e.g., [7] 3GPP RAN2#121bis report), the following agreement has been made regarding LTM:

[0430] From the RAN2 perspective, in order to achieve shared preamble resources among multiple UEs, it is beneficial that information identifying the allocated CFRA resources (i.e., SS / PBCH index, RACH opportunity and random access preamble index) can be indicated in the PDCCH order (as a traditional intra-cell PDCCH order).

[0431] The RRC RACH configuration for early TA acquisition (eg including whether RAR needs to be received) is specific to each target cell and is sent separately (separate IE) from the candidate cell configuration (the part that needs to be applied at cell handover).

[0432] R2 assumes that Early TA RACH option 3 (with RAR from candidate cells) is not needed in Rel-18.

[0433] R2 assumes that the RRCReconfigurationComplete message is always sent at every LTM execution.

[0434] In RACH-based LTM, the target cell is aware of the arrival of the UE based on the reception of the preamble in CFRA and based on the reception of Msg3 / MsgA in CBRA, similar to conventional HO.

[0435] In RACH-free LTM, the target cell is aware of the arrival of the UE based on the reception of the first UL transmission from the UE.

[0436] In RACH-free LTM, RRCReconfigurationComplete can be the content of the first UL MAC PDU / transmission to indicate the UE arrival, i.e. no new signaling needs to be introduced to indicate the UE arrival (for MCG handover case)

[0437] For RACH-based LTM, the UE considers that the LTM execution step is successfully completed when RACH is successfully completed.

[0438] For RACH-free LTM, the UE considers that the LTM execution step is successfully completed when the UE determines that the NW has successfully received its first UL data.

[0439] The following behavior of the LTM monitoring timer is agreed upon:

[0440] -1: After receiving the LTM cell switching MAC CE, the UE immediately starts the LTM monitoring timer;

[0441] -2: After the LTM cell handover is successfully completed, the UE immediately stops the LTM monitoring timer;

[0442] -3: If the LTM monitoring timer for MCG expires, then as a baseline, the UE considers LTM failure and initiates RRC re-establishment. (SCG handover is for further study)

[0443] The LTM monitoring timer is an RRC layer timer.

[0444] In case of RLF or LTM execution failure (for MCG), RAN2 intends to support fast recovery to candidate cells through LTM execution.

[0445] Although configured with LTM candidate cells, the UE may also execute any L3 handover command sent by the network. R2 assumes that any problems due to race conditions between LTM execution and RRC reconfiguration (e.g., L3 HO command) can be avoided by the network, for example, by avoiding sending LTM handover command and L3 HO command in the same TB.

[0446] In the 3GPP RAN2#122 meeting (e.g., [8] 3GPP RAN2#122 report), the following agreement was made regarding TA maintenance of candidate cells for LTM:

[0447] Dynamic grant can be used without RACH LTM for the first UL data transmission to the target cell:

[0448] -After LTM cell switching, the UE immediately monitors the PDCCH for dynamic scheduling from the target cell.

[0449] - After the cell switching decision, R2 immediately assumes that the source DU informs the target DU of the selected beam so that the target DU can start scheduling dynamic UL grants.

[0450] Configured grants may be used for RACH-free LTM for the first UL data transmission to the target cell, the UE selects the configured grant opportunity, which is associated with the beam indicated in the LTM MAC CE (set by the source cell). Additional optimizations are for further study

[0451] If TA maintenance etc. for candidate cells in the UE is required, the TAs associated with the candidate cells may be maintained during LTM (exactly which cells decision phase 3 is pending).

[0452] In 3GPP specification 38.211 (e.g., [9] 3GPP 38.211 v17.1.0), timing advance is introduced:

[0453] N TA Timing advance between downlink and uplink; see clause 4.3.1

[0454] N TA,偏移 Fixed offset used to calculate timing advance; see clause 4.3.1

[0455] 4.3.1 Frame and Subframe

[0456] Downlink, uplink and sidelink transmissions are organized into f =(Δf max N f / 100)·T c = 10ms duration frame, each frame consists of T sf =(Δf max N f / 1000)·T c =1 ms duration. The number of consecutive OFDM symbols per subframe is Each frame is divided into two equally sized half-frames of five sub-frames, each with half-frame 0 consisting of sub-frames 0-4 and half-frame 1 consisting of sub-frames 5-9.

[0457] On a carrier, there is a set of frames in the uplink and a set of frames in the downlink.

[0458] The uplink frame number i for transmission from the UE should precede the start of the corresponding downlink frame at the UE Start, where

[0459] -NTA and N TA,偏移 Given by clause 4.2 of [5, TS 38.213], except for msgA transmission on PUSCH, where N TA =0;

[0460] - is derived from the higher-level parameters TACommon, TACommonDrift, and TACommonDriftVariation (if configured), otherwise

[0461] - is calculated by the UE based on the UE position and the serving satellite ephemeris related higher layer parameters (if configured), otherwise

[0462] Fig.12 It is from 3GPP 38.211v17.1.0 Figure 4 .3.1-1: Reproduction of uplink-downlink timing relationship.

[0463] In New Radio (NR), a User Equipment (UE) performs a handover procedure to switch from one cell (e.g., a source cell) to another cell (e.g., a target cell). The UE performs the handover procedure in response to Radio Resource Control (RRC) signaling transmitted by the network. The RRC signaling contains the cell information of the target cell. The network determines to initiate the handover procedure based on the UE's measurement report. The change of the Primary Cell (PCell) and the Primary Secondary Cell (PSCell) via a reconfiguration with synchronization (e.g., involving layer 3 RRC messages) involves higher latency and more overhead than L1 / L2 signaling (e.g., beam switching mobility). In addition, in operation on frequency range 2 (FR2), frequent Secondary Cell Group (SCG) changes will occur, which may also result in high latency for UE-network (NW) communications when L3 handover is used. Therefore, in NR mobility enhancement (e.g., [3] RP-212710 New Work Item Description (WID) for further NR mobility enhancement), the goal of the work item is to specify mechanisms and procedures (e.g., L1 / L2 triggered mobility procedures, or layer 1 / layer 2 triggered mobility (LTM) procedures) for dynamic switching mechanisms among serving cells (including special cells (SpCells) and / or secondary cells (SCells)) based on L1 / L2 signaling. The serving cell may include a target cell for the LTM procedure and one or more secondary cells (to be added or released) in the LTM procedure. The LTM procedure may consist of first information and second information provided by the next generation Node B (gNB) of the source cell. The first information may contain or indicate candidate cell information (e.g., candidate cell configuration) (via RRC message). The first information may contain or indicate one or more RRC reconfiguration messages associated with one or more candidate cells (or candidate cell groups). For example, the first information may contain or indicate a cell configuration and / or random access (random access channel (RACH)) configuration for the one or more candidate cells. The first information may contain one or more RRCReconfiguration messages, each message being used for a candidate (cell) configuration associated with a candidate cell. The second information may not be an RRC or L3 message (e.g., may contain a physical downlink control channel (PDCCH) and / or a media access control (MAC) control element CE), and may instruct the UE to perform an LTM procedure to a candidate cell (group) (one or more candidate cells in the first information).The second information may be an LTM handover command or a cell handover command (e.g., a downlink control indicator (DCI) and / or a MAC CE). The candidate cell may be a target cell for the LTM procedure. Each of the one or more candidate cells may be associated with an identity or index (e.g., a candidate index). The second information may indicate a candidate index of the candidate cell. The candidate cell of the UE is not a serving cell of the UE. The candidate cell of the UE is a candidate to be a serving cell (e.g., a PCell or SpCell) of the UE.

[0464] For LTM, both RACH-based and RACH-less LTM will be supported.For RACH-based LTM, the UE initiates / performs a random access procedure to the target cell in the LTM procedure (in response to receiving a cell handover command to handover to the target cell).

[0465] For RACH-free LTM, the UE may not initiate / perform a random access procedure to the target cell in the LTM procedure in response to or after receiving a cell handover command to handover to the target cell. The UE may determine whether to perform a random access procedure to the target cell (to obtain a timing advance (TA)) in response to a cell handover command (e.g., second information) based on whether there is a valid TA associated with the target cell (stored in the UE). The valid TA associated with the target cell may be a TA associated with the candidate cell (stored in the UE or maintained by the UE). The UE may perform (early) TA acquisition to the target cell (or candidate cell) to obtain the TA (before initiating the LTM procedure). Alternatively, the UE may perform UE-based TA measurement to obtain the TA of the target cell (or candidate cell). When the UE maintains or stores the TA associated with the candidate cell, the validity of the TA needs to be ensured, and the TA may need to be updated or released / discarded if or when the TA is not valid. In addition, due to the storage capacity of the UE (e.g., the number of stored TAs in the stored TA list for the candidate cell is limited) or configuration limitations, the UE may store or maintain TAs for the maximum number of candidate cells. In order to maintain the TA while adding / updating the TA for the candidate cells, a problem may arise as to how to update or whether to inform the network about the storage condition of the TA in order to have aligned TA maintenance knowledge between the network and the UE.

[0466] By the present invention, a method and system for handling stored TA and timer maintenance for candidate cells are introduced, as described in detail below.

[0467] ● Handling of TA / Time Alignment Timer (TAT) for candidate cells

[0468] ■ Assume that the number of stored TAs and / or TATs for candidate cells is limited

[0469] ◆For stored TAs for candidate cells:

[0470] ●How / when to clear stored TA?

[0471] ■Should the stored TA be cleared when the corresponding TAT expires?

[0472] ■Does the serving cell change or UE status change affect the stored TA?

[0473] ●Whether / how to update the stored TA?

[0474] • How / when to replace the stored TA with the TA for another candidate cell?

[0475] ■Which one to replace?

[0476] ◆For the running TAT for the candidate cell:

[0477] ●How / when to stop TAT?

[0478] ●How / when to restart TAT?

[0479] ◆Should the maximum number be reported to the network, eg as a UE capability?

[0480] ◆Should the current number be reported to the network?

[0481] Should the UE report to the network which candidate cells have (valid) stored TAs? For example, UE initiates or NW requests

[0482] ■The number of stored TAs has reached the maximum and an early TA PDCCH command has been received

[0483] ■The number of stored TAs has reached the maximum and LTM is performed from the source cell to the target cell

[0484] ◆The TA of the source cell will be stored?

[0485] Clear stored TA

[0486] One concept of the present invention is that the UE may determine whether to clear or discard a (stored) TA associated with a (UE's) candidate cell. To clear or discard a stored TA for a (UE's) candidate cell, the UE may remove, clear, release or discard the stored TA from a list (or set) of stored TAs for (UE's) candidate cells. The list (or set) of stored TAs may not contain a TA for a (UE's) serving cell.

[0487] The UE may determine whether to clear / release the stored TA based on at least one of the following:

[0488] - the status of the timer associated with the stored TA;

[0489] -UE performs RRC re-establishment;

[0490] -UE enters RRC_IDLE or RRC_INACTIVE state;

[0491] -Service cell change;

[0492] - UE storage capacity to store the TA of the cell; and / or

[0493] - The remaining validity time of the stored TA

[0494] For example, for a UE having a stored TA associated with a candidate cell (of the UE), the UE may determine whether to clear / release / discard the stored TA based on the state of a timer (at least associated with the (stored) TA associated with the candidate cell). For example, the UE may clear or discard the stored TA associated with the candidate cell when the timer expires or in response to the timer expiring. The timer may be a time alignment timer (or TA timer or TAT) associated with at least the candidate cell. Additionally and / or alternatively, the timer may be associated with a timing advance group (TAG) associated with at least the candidate cell. Additionally and / or alternatively, the UE may start or restart the timer when or in response to obtaining, storing or updating the TA associated with the candidate cell. The value or length of the timer associated with different candidate cells (of the UE) may be independently configured (by the network) or may be the same (e.g., may not be different). The UE may keep or maintain the stored TA associated with the serving cell when or in response to the TAT associated with the serving cell expiring.

[0495] For example, the UE may (re)start the timer in response to obtaining, storing or updating a TA associated with a candidate cell or transmitting a report to the network. The report may contain or indicate (information about) the TA and / or the candidate cell. Additionally and / or alternatively, the UE may (re)start the timer in response to initiation or completion of (early) TA acquisition on the candidate cell (for obtaining the TA). The UE may (re)start the timer in response to receiving a PDCCH command from the network indicating initiation of TA acquisition. The UE may stop the timer associated with the candidate cell in response to the UE clearing or discarding a stored TA associated with the candidate cell.

[0496] The UE may clear or discard a stored TA associated with a candidate cell when or in response to a candidate (cell) reconfiguration associated with the candidate cell. The candidate (cell) reconfiguration may release or remove the candidate cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell when or in response to a candidate (cell) reconfiguration associated with the candidate cell. The candidate (cell) reconfiguration may not release or remove the candidate cell. For another example, the UE may stop the timer in response to a candidate (cell) reconfiguration associated with the candidate cell. The candidate (cell) reconfiguration may release or remove the candidate cell. Alternatively, the UE may not stop the timer in response to a reconfiguration with synchronization or LTM switching the SpCell to the (UE's) candidate cell.

[0497] The candidate (cell) reconfiguration associated with the candidate cell may be a release of the candidate cell configuration (associated with the candidate cell). Additionally and / or alternatively, the candidate (cell) reconfiguration associated with the candidate cell may be a removal of the candidate cell from a candidate cell list.

[0498] Alternatively, the UE may not clear or discard (or may keep or maintain) the stored TA associated with the candidate cell in response to the expiration of the timer. For example, the UE may store or keep or maintain the TA after the expiration of the timer (as long as the UE has storage capacity to store the TA).

[0499] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with a candidate cell in response to a serving cell (e.g., PCell or SpCell) change of the UE. For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or a TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell in response to a serving cell change or a serving cell release.

[0500] The serving cell change may be in response to a reconfiguration with synchronization (eg, received from the network).

[0501] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with the candidate cell in response to receiving an RRC message (e.g., MobilityFromNRCommand). For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or a TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell in response to receiving an RRC message (e.g., MobilityFromNRCommand).

[0502] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with the candidate cell in response to receiving an RRC message (e.g., RRCReconfiguration) containing reconfigurationWithSync. For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or a TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell in response to receiving an RRC message (e.g., RRCReconfiguration) containing reconfigurationWithSync.

[0503] The serving cell change may be in response to an LTM procedure.

[0504] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with the candidate cell in response to receiving second information (e.g., a cell switching command) indicating or initiating an LTM procedure to (change the PCell or SpCell to) a second candidate cell (of the UE). For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or a TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell in response to receiving second information (e.g., a cell switching command) indicating an LTM procedure to a second candidate cell (of the UE). The second candidate cell may be a candidate cell associated with a stored TA. Alternatively, the second candidate cell may be different from the candidate cell associated with a stored TA.

[0505] The serving cell change may be in response to RRC re-establishment.

[0506] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with the candidate cell when performing RRC re-establishment. For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell when performing RRC re-establishment.

[0507] The serving cell change may be in response to UE-initiated LTM (eg, conditional LTM) or conditional reconfiguration (eg, conditional handover).

[0508] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with a candidate cell when performing a UE-initiated LTM procedure or conditional reconfiguration. For example, the UE may clear or discard a stored TA in response to a serving cell release. The candidate cell may share the same TAG and be associated with the same TAG as the serving cell. The stored TA associated with the candidate cell may be a TAG or a TA associated with the serving cell. Alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with the candidate cell when performing a UE-initiated LTM procedure or conditional reconfiguration.

[0509] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with a candidate cell in response to completion of LTM (or handover, or reconfiguration with synchronization) to the candidate cell. In response to handover of the UE's SpCell to the candidate cell, the UE may clear or discard a stored TA of the candidate cell (and apply the stored TA as the TA for the SpCell or primary timing advance group (pTAG)). Additionally and / or alternatively, the UE may clear or discard a stored TA associated with a first candidate cell (of the UE) in response to completion of LTM to a second candidate cell (of the UE) or a reconfiguration (handover) procedure with synchronization. Additionally and / or alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with a first candidate cell (of the UE) in response to completion of LTM to a second candidate cell (of the UE) or a reconfiguration (handover) procedure with synchronization.

[0510] Additionally and / or alternatively, the UE may clear or discard a stored TA associated with a candidate cell in response to the UE entering (from RRC_CONNECTED to) an RRC_INACTIVE state or an RRC_IDLE state. Additionally and / or alternatively, the UE may not clear or discard (or may keep or maintain) a stored TA associated with a candidate cell in response to the UE entering (from RRC_CONNECTED to) an RRC_INACTIVE state or an RRC_IDLE state. The UE may keep or maintain a stored TA associated with a serving cell in response to the UE entering (from RRC_CONNECTED to) an RRC_INACTIVE state or an RRC_IDLE state.

[0511] Update TA: Update the same TA or replace the old TA with a new candidate cell TA

[0512] Additionally and / or alternatively, the UE may update or renew a stored TA associated with (the UE's) candidate cell. If or when the stored TA is invalid or a timer associated with the TAT expires, the UE may update or renew a stored TA associated with the candidate cell. If or when the UE is reconfigured with a candidate cell configuration or reconfigured with an LTM configuration, the stored TA may be considered invalid. For example, the UE may trigger or initiate a TA acquisition procedure to the candidate cell in response to the expiration of a timer associated with the TA associated with the candidate cell. The TA acquisition procedure may include transmitting a random access preamble to the candidate cell. The TA acquisition procedure may include receiving a message or signaling (e.g., a random access response, or a MAC CE or DCI) indicating a TA associated with the candidate cell. Additionally and / or alternatively, the TA acquisition procedure may include applying a new TA value to the stored TA. The new TA value may be derived (by the UE) from the serving cell TA or TAG. The new TA value may be derived from the reconfigured (LTM) candidate cell configuration or the reconfigured TAG.

[0513] Replace the TA with the TA of another candidate cell

[0514] Determine which TA to discard / replace

[0515] Additionally and / or alternatively, the UE may discard or clear a first stored TA associated with a first candidate cell (of the UE) in response to adding or storing a second TA associated with a second candidate cell (of the UE). The UE may determine a first stored TA to be discarded or cleared among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on an id or index associated with the TA. For example, the first candidate cell may be associated with a candidate cell configuration having a lowest (or highest) candidate cell id or index (e.g., an LTM candidate id). Additionally and / or alternatively, the UE may determine which TA to discard or clear among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on a state of a timer associated with the TA. For example, the UE may discard or clear a first TA in response to adding or storing a second TA based at least on the expiration of a timer associated with the first TA. Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared among all stored TAs (of a list or set of stored TAs) associated with (one or more) candidate cells (of the UE) based at least on the validity of the stored TA.

[0516] Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared from among all stored TAs (of a list or set of stored TAs) associated with (one or more) candidate cells (of the UE) based at least on whether each of the stored TAs is valid (or not valid).

[0517] Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on an id or index associated with the (UE's) candidate cell. For example, the UE may discard or clear a first TA associated with a first candidate cell (of the UE) in response to adding or storing a second TA, wherein the first candidate cell is associated with a lowest id (e.g., a candidate configuration id) among the (UE's) candidate cells having (valid or invalid) stored TAs.

[0518] Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on the remaining validity time of each of the stored TAs. Additionally and / or alternatively, the UE may discard the first TA (among all stored TAs associated with the candidate cell) having the shortest remaining validity time (e.g., the timer associated with the first TA is closest to timer expiration) in response to adding or storing the second TA.

[0519] Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on the (absolute) value of each of the stored TAs. Additionally and / or alternatively, the UE may discard a first TA (among all stored TAs associated with the candidate cells) having a maximum (absolute) TA value (e.g., the candidate cell associated with the first TA is farthest from the UE) in response to adding or storing the second TA.

[0520] Additionally and / or alternatively, the UE may discard or clear the (exactly) first TA stored in the list (or set) of stored TAs (in response to adding or storing a second TA associated with a second candidate cell (of the UE)).

[0521] Additionally and / or alternatively, the UE may determine a first stored TA to be discarded or cleared among all stored TAs associated with (one or more) candidate cells (of the UE) based at least on whether each of the stored TAs has been used or applied (to the serving cell). For example, the UE may discard or clear the least used stored TA. If or when the storage capacity of the UE (e.g., the list (or set) of stored TAs for candidate cells) can accommodate all stored TAs (and (additional) TAs), the UE may not discard or clear (or may keep or maintain) (any) TA associated with the (UE's) candidate cell in response to adding or storing the (additional) TA. If or when the storage capacity of the UE (e.g., the list (or set) of stored TAs for candidate cells) cannot accommodate all stored TAs (and additional TAs), the UE may discard or clear the TA associated with the (UE's) candidate cell in response to adding or storing the (additional) TA.

[0522] Fig.13 An example is shown in FIG. 1 , where the UE may store / maintain a maximum number of stored TAs (e.g., 2). The UE stores a first TA, TA1, for candidate cell 1 and a second TA, TA2, for candidate cell 2 (before timing t1). The UE obtains a third TA for candidate cell 3 at timing t1 (e.g., via a TA acquisition procedure). The UE may determine to discard / clear TA1 based on candidate cell 1 being associated with the lowest LTM candidate id. The UE stores TA3 for candidate cell 3 and (maintains) TA2 for candidate cell 2.

[0523] Fig.14Another example is shown in FIG. 1 . The UE stores (maximum) 3 TAs, TA1, TA2, and TA3 for candidate cells 1, 2, and 3, respectively (before timing t1). TA1 is valid and TA2 and TA3 are invalid (e.g., a timer expires or the candidate cell or an associated serving cell has been reconfigured). The UE receives or obtains TA4 associated with candidate cell 4. The UE may determine to remove or clear or discard TA2 and store TA4 for candidate cell 4 (e.g., based on TA2 being associated with a candidate cell having a lowest LTM candidate configuration id among the candidate cells having stored invalid (or valid) TAs).

[0524] For another example, (when the storage capacity cannot accommodate the additional TA,) the UE may (first) determine whether there is an invalid stored TA among all stored TAs. When there is (one or more) invalid stored TAs, the UE discards or clears one of the invalid stored TAs (e.g., the least used, or the (exactly) first invalid TA in the list (or set) stored among (one or more) invalid stored TAs). Additionally and / or alternatively, when there is no invalid stored TA, the UE discards or clears one of all stored TAs (e.g., the least used, or the (exactly) first invalid TA in the list (or set) stored among (one or more) invalid stored TAs).

[0525] When the maximum value (of storage capacity) is reached, TA is not obtained

[0526] Additionally and / or alternatively, if or when the number of stored TAs of the UE has reached the maximum number of stored TAs, the UE may not perform TA acquisition for (the UE's) candidate cells. The maximum number of stored TAs may be the number of TAs for candidate cells that the UE may store or maintain at (the same) time.

[0527] For example, the UE may determine whether to perform TA acquisition in response to receiving a PDCCH command for TA acquisition on a candidate cell (of the UE) from the NW based at least on whether the number of stored TAs has reached a maximum number. If the number of stored TAs has reached a maximum, the UE may not perform TA acquisition. If the number of stored TAs has not reached a maximum, the UE may perform TA acquisition on the candidate cell.

[0528] Alternatively, the UE may not (itself) initiate TA acquisition on (UE's) candidate cells if or when the number of stored TAs has reached a maximum. The UE may initiate TA acquisition (commanded by the network) if or when the number of stored TAs has reached a maximum. The UE may not store or have not yet obtained a TA for a candidate cell before receiving a PDCCH command or performing TA acquisition.

[0529] When triggering / initiating LTM, UE stores the previously left serving cell / TAG / / stores the source cell TA

[0530] Additionally and / or alternatively, the UE may store or hold or maintain a TA associated with the source cell when initiating or triggering an LTM procedure to (handover from the source cell to) a candidate cell (of the UE). The source cell may be one of the candidate cells of the UE. If the number of stored TAs has reached a maximum, the UE may not store or hold or maintain (or may clear or discard) the TA associated with the source cell. Alternatively, the UE may store or hold or maintain the TA associated with the source cell after applying the TA associated with the candidate cell. The UE may replace (e.g., discard or clear) a stored TA associated with a candidate cell (e.g., a target cell of the LTM) with a TA associated with the source cell. When the number of stored TAs has reached a maximum, the UE may determine the stored TA associated with the candidate cell (of the UE) to be discarded or cleared (and store the TA associated with the source cell) (e.g., based on the method described above).

[0531] Additionally and / or alternatively, the UE may store or retain or maintain one or more TAGs (of TAs) associated with one or more serving cells or source cells when initiating or triggering an LTM procedure to a (UE's) candidate cell. If the number of stored TAs has reached a maximum, the UE may not store or retain or maintain (or may clear or discard) the TA associated with the source cell.

[0532] To store the TA for the candidate / source cell, the UE may add / keep / maintain the TA in the list (or set) of stored TAs for the candidate cells.

[0533] Indicates the replaced TA or updated TA or currently stored TA to the NW

[0534] Another concept of the present invention is that the UE may transmit a report to the network to indicate information associated with a stored / maintained / valid TA associated with one or more candidate cells (of the UE) and / or information associated with one or more candidate cells (of the UE) with a stored / maintained / valid TA. The report may be a TA report or a stored TA status report. The report may be a measurement report.

[0535] The UE may trigger the transmission of a report in response to a change or update of a stored TA of a (UE's) candidate cell or a change or update of a list (or set) of stored TAs of (UE's) candidate cells. For example, the UE may transmit a report to the network in response to obtaining or storing a (new) TA associated with a (UE's) candidate cell. The (UE's) candidate cell or the (new) TA associated with the (UE's) candidate cell may not be reported or indicated to the network (in a previous report). For another example, the UE may (trigger) transmit a report to the network in response to clearing or discarding a stored TA associated with the (UE's) candidate cell. For another example, the UE may (trigger) transmit a report to the network in response to a stored TA associated with the (UE's) candidate cell becoming invalid or being deemed invalid. For another example, the UE may (trigger) transmit a report to the network in response to the TAT associated with the (UE's) candidate cell expiring. For another example, the UE may (trigger) transmit a report to the network in response to clearing a stored TA associated with the (UE's) candidate cell. For another example, the UE may (trigger) transmit a report to the network in response to replacing a stored TA associated with a (UE's) candidate cell.

[0536] Additionally and / or alternatively, the UE may trigger a report indicating a stored (and / or valid) TA in response to (receipt of) signaling indicated by the network. The UE may transmit the report in response to receiving signaling (e.g., DCI or RRC message or MAC CE) from the network. The signaling may indicate a request for a report.

[0537] Additionally and / or alternatively, the UE may trigger the transmission of the report based on a periodicity or a timer. The timer may be a reporting timer. If or when the timer expires, the UE may trigger the report. The UE may start or restart the timer when the UE triggers or transmits the report to the network.

[0538] Fig.15 An example is shown in FIG. UE stores TA1 for candidate cell 1 and TA2 for candidate cell 2 before timing t1. At timing t1, UE obtains / stores TA3 for candidate cell 3. In response to obtaining or storing TA3, UE may trigger transmission of a report indicating TAs associated with one or more candidate cells to the NW.

[0539] Fig.16 Another example is shown in FIG. 1 . The UE stores TA1 for candidate cell 1 and TA2 for candidate cell 2. At timing t1, TA2 becomes invalid (e.g., timer expires or UE is reconfigured). The UE may discard or clear the stored TA2 in response to considering TA2 invalid. In response to discarding / clearing TA2, the UE may trigger transmission of a report to the network (indicating a change in the stored TA).

[0540] Contents of the report

[0541] The report may contain or indicate (UE's) candidate cells with (valid) stored TAs. Additionally and / or alternatively, the report may contain or indicate the number of (valid) stored TAs associated with candidate cells stored in the UE. Additionally and / or alternatively, the report may contain or indicate the number of (UE's) candidate cells associated with (valid) stored TAs stored in the UE. The report may contain or indicate (UE's) candidate cells with stored TAs removed / cleared. The report may contain or indicate (UE's) candidate cells without (valid) stored TAs.

[0542] The report may contain or indicate a (valid) stored TA associated with the candidate cells of the UE. Alternatively, the report may not contain or indicate a (valid) stored TA associated with the candidate cells of the UE.

[0543] The report may contain a flag indicating whether a report indicating an added TA or cleared TA for a (UE's) candidate cell is triggered. Additionally and / or alternatively, a flag may be indicated for each candidate id or candidate cell (individually). Additionally and / or alternatively, the report may contain a field indicating a candidate configuration (e.g., LTM candidate id) associated with the (UE's) candidate cell in which the TA is stored, removed or cleared. Additionally and / or alternatively, the report may contain a bitmap indicating a candidate configuration associated with the (UE's) candidate cell and having a stored or valid or removed or cleared TA. Each bit of the bitmap may correspond to the (UE's) candidate cell. Each bit of the bitmap may indicate whether the (UE's) candidate cell (corresponding to the bit) has a (valid) stored TA. The report may contain a bit indicating whether the (UE's) candidate cell has a (valid) stored TA.

[0544] The report may contain or indicate a measurement result of a candidate cell (of the UE). The measurement result may be associated with a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS) or a (activated) transmission configuration indicator (TCI) state of the candidate cell (e.g., an L1 measurement). The measurement result may be a reference signal received power (RSRP) (e.g., an L1 or L3 RSRP measurement). The report may contain an SSB or CSI-RS or (activated) TCI state associated with the measurement result.

[0545] The report can be a MAC CE or an RRC message.

[0546] Indicates newly added TA or all stored TAs

[0547] The report may indicate (all) candidate cells (of the UE) that the TA has stored (and / or available) in the UE. Alternatively, the report may indicate one or more candidate cells (of the UE) that the TA has added or removed (since the last report). The report may report the delta, or the difference in the stored TA status compared to the last time the report was transmitted.

[0548] Fig.17 Another example is shown in FIG. 1 . At timing t0, the UE reports to the NW a TA report indicating that the UE stores TAs (TA1, TA2) for candidate cell 1 and candidate cell 2. At timing t1, the UE obtains / maintains TA3 for candidate cell 3. The UE may trigger transmission of a second report to the NW at timing t2. The UE may report all candidate cells (e.g., candidate cells 1, 2, 3) to the NW in the second report. Alternatively, the UE may report candidate cell 3 to the NW in the second report (since the TA storage state of candidate cell 3 has changed since the last transmission of the report).

[0549] Indicate UE storage capacity to NW

[0550] Indicates the current number of stored

[0551] Additionally and / or alternatively, the report may contain or indicate to the network the storage capacity of the UE (e.g., the maximum number of stored TAs in the list (or set) of stored TAs). The storage capacity may be the maximum number of TAs associated with candidate cells that the UE may store / maintain. The storage capacity may be the maximum number of TAs (or TA values) (associated with the UE's candidate cells) that may be stored by the UE. Alternatively, the report may not indicate the storage capacity of the UE. The storage capacity may be indicated in a different message than the report (e.g., the different message may be an RRC message). The storage capacity may be the UE's ability to store TAs (for candidate cells).

[0552] Additionally and / or alternatively, the report may contain or indicate the number of (valid) TAs (associated with the UE's candidate cells) currently stored by the UE. Additionally and / or alternatively, the report may contain or indicate the TA associated with each reported candidate cell stored by the UE.

[0553] Fig.18A An example is shown in . The report may indicate one or more candidate configuration IDs associated with one or more candidate cells. The report may indicate the number of candidate cells reported in the report.

[0554] Fig.18B Another example is shown in . The report may indicate a field / flag indicating whether the report instructs the UE to add or clear a stored TA for the indicated configured / associated candidate cell. Fig.18CAnother example is shown in . A report may indicate whether the report contains a TA value for each candidate cell that has been reported.

[0555] The network determines whether to send PDCCH order / TA in CSC based on UE report / update on TA

[0556] Additionally and / or alternatively, the network may determine whether to initiate TA acquisition on the candidate cell for the UE based at least on the report. If or when the UE does not store a TA for the candidate cell or the stored TA is invalid or not aligned with the network, the network may initiate TA acquisition for the UE on the candidate cell.

[0557] Additionally and / or alternatively, the network may determine whether to indicate the TA in the second information to the UE in an LTM procedure to the candidate cell (eg, in a cell handover command) based on whether the UE has a valid stored TA for the candidate cell.

[0558]

[00106] With respect to the embodiments, examples and concepts detailed above and herein, the following aspects and embodiments are possible.

[0559] The TA associated with the candidate cell may be provided / indicated by the network via first information (e.g., candidate cell configuration). The TA associated with the candidate cell may be obtained / stored by the UE before receiving an LTM cell switching command indicating switching to the candidate cell. Additionally and / or alternatively, the TA may be provided / indicated by the network via second information (e.g., cell switching command). Alternatively, the (stored) TA associated with the candidate cell may not be provided / indicated by the network (via the second information or via the cell switching command). Additionally and / or alternatively, the UE may perform TA acquisition for the candidate cell before initiating the LTM procedure (e.g., before receiving the second information or the cell switching command) to obtain the TA associated with the candidate cell. The TA acquisition (procedure) for the candidate cell may contain or include the network transmitting a PDCCH command (or similar to a PDCCH command) message to the UE. The message may indicate that the UE initiates a TA acquisition procedure or obtains a TA associated with the candidate cell. The TA acquisition (procedure) for the candidate cell may contain or include the UE transmitting a (random access) preamble to the candidate cell. TA acquisition for the candidate cell may contain or include the UE receiving a message (or signaling) containing or indicating the TA associated with the candidate cell (eg, a random access response (RAR), or a message similar to RAR, or a MAC CE, or a DCI).

[0560] Additionally and / or alternatively, the UE may obtain or derive a TA associated with the candidate cell.

[0561] Additionally and / or alternatively, the UE may obtain or derive the TA associated with the candidate cell by storing the TA of the TAG associated with the (previous) serving cell. The (previous) serving cell may be the candidate cell or share the same TA with the candidate cell.

[0562] TA can be the timing difference between the uplink and downlink of the cell. TA can be the TA value. TA can be N TA TA may be a TAG id. TA may be a timing advance command (TAC).

[0563] To discard or clear the TA associated with the candidate cell, the UE may consider the TA invalid and / or the UE may not apply the TA on the candidate cell in response to performing the LTM procedure on the candidate cell.

[0564] The candidate cell may be a (primary) cell in a candidate cell group configuration.

[0565] The candidate cell group configuration may be an RRC reconfiguration message.

[0566] The UE may perform TA acquisition instructed by the network or initiated by the UE (itself) (e.g., for a candidate cell). TA acquisition may be an early TA acquisition (e.g., early uplink (UL) synchronization) for a candidate cell before receiving a cell handover command for an LTM procedure. TA acquisition may contain RAR-based RACH or RAR-less RACH. RAR may indicate TA information (e.g., TA or TAC) associated with a candidate cell.

[0567] A RACH without RAR may contain a random access response. A random access response may not contain a RAR. The RAR may be the MAC payload of the random access response. A RACH without RAR may contain (only) the MAC subheader of the random access response.

[0568] The UE may be configured with RAR-less RACH for the candidate cell. The RAR-less RACH may contain a RAR-less TA acquisition mechanism.

[0569] The serving cell / candidate cell configuration may be / include a RACH configuration for a random access procedure on the candidate cell. The RACH configuration may indicate a search space id and / or a RACH opportunity and / or a preamble index.

[0570] The TA information associated with the candidate cell may be a TA command (timing advance command) associated with the candidate cell or a N TA or TAG.

[0571] The TA information of the candidate cell may be the timing difference between the uplink and downlink associated with the candidate cell.

[0572] The PDCCH order initiating the random access procedure on the candidate cell may contain or indicate a bandwidth part (BWP) (of the candidate cell).

[0573] The PDCCH order initiating the random access procedure on the candidate cell may contain or indicate a cell / candidate index (of the candidate cell or candidate cell configuration).

[0574] The PDCCH order initiating a random access procedure on a candidate cell may contain or indicate a RACH configuration (associated with the candidate cell or candidate cell configuration).

[0575] The first PDCCH opportunity (when the UE starts the window) may be the first PDCCH opportunity associated with a cell radio network temporary identifier (C-RNTI) or a random access (RA)-radio network temporary identifier (RNTI) (after preamble transmission or after an offset after preamble transmission). The first PDCCH opportunity may be the first PDCCH opportunity associated with a (type 1) common search space or a UE-specific search space.

[0576] L1 / L2 triggered mobility (LTM) can be an intra-distributed unit (DU) LTM. Alternatively, LTM can be an inter-DU or inter-centralized unit (CU) LTM.

[0577] LTM may include the network transmitting first information and second information to the UE. The first information may be an RRC message indicating one or more candidate cells (or a cell group or one or more RRC reconfigurations indicating a candidate configuration). The first information may contain one or more Cellgroupconfig or one or more RRCReconfiguration messages. The second information may be L1 or L2 signaling and / or a cell switching command (e.g., PDCCH and / or MAC CE). The UE may initiate LTM or start a cell switching (to one or more candidate cells) in response to the second information.

[0578] The first information may contain RACH configuration and / or cell configuration for the one or more candidate cells. The network may indicate the RACH configuration for the corresponding candidate cell in a PDCCH order for TA acquisition of the candidate cell.

[0579] The candidate cell list may contain a list of candidate cells (eg, a list of candidate cell configurations indicating the candidate cell list).

[0580] The candidate cell configuration may be (part of) the RRC reconfiguration message.

[0581] The RRC message may be RRCReconfiguration.

[0582] The UE may consider the LTM to be successfully completed when an acknowledgement is received from the network (e.g., the target gNB). The acknowledgement may be in response to a completion message associated with the LTM transmitted by the UE. Additionally and / or alternatively, the UE may consider the LTM to be successfully completed when a random access procedure associated with (or initiated for) the LTM is successfully completed.

[0583] The UE may apply the stored (and / or valid) TA associated with the candidate cell to the candidate cell during or at the start of the LTM procedure to the candidate cell.

[0584] Any combination of the concepts or teachings above or herein may be fully or partially combined or formed into new embodiments. The disclosed details and embodiments may be used to at least (but not limited to) solve the problems mentioned above and herein.

[0585] See also Fig.19 , with respect to such and other concepts, systems and methods of the present invention, a method 1000 for a UE in a wireless communication system includes storing or maintaining a TA for a candidate cell (step 1002), and clearing the TA of the candidate cell in response to at least one of: expiration of a timer; reconfiguration of a candidate configuration associated with the candidate cell; the UE entering an RRC_IDLE state or an RRC_INACTIVE state; and / or the UE switching its SpCell to a second candidate cell (step 1004).

[0586] In various embodiments, the candidate cells are associated with an LTM configuration.

[0587] In various embodiments, the UE starts a timer in response to obtaining the TA of the candidate cell.

[0588] In various embodiments, the UE starts a timer in response to transmitting a report indicating the TA to the network.

[0589] In various embodiments, the UE starts the timer in response to receiving PDCCH signaling from the network indicating an (early) TA acquisition procedure to obtain the TA of a candidate cell.

[0590] In various embodiments, the UE starts a timer in response to a reconfiguration of a candidate configuration associated with a candidate cell.

[0591] In various embodiments, the UE stops the timer in response to initiation or completion of the LTM procedure to the candidate cell.

[0592] In various embodiments, the UE stops the timer in response to initiation or completion of the LTM procedure to the second candidate cell.

[0593] In various embodiments, the UE stops the timer in response to the TA becoming invalid.

[0594] In various embodiments, the UE clears the TA by removing the TA from the list (or set) of stored TAs for candidate cells.

[0595] In various embodiments, the candidate cell is not a serving cell.

[0596] In various embodiments, the UE does not clear the TA in response to a MAC reset or in response to initiation of an LTM procedure.

[0597] In various embodiments, TA is N TA or TAG.

[0598] In various embodiments, the UE clears the TA by considering the TA as invalid.

[0599] In various embodiments, the PDCCH signaling is a PDCCH order.

[0600] In various embodiments, the candidate configuration is a L1 / L2 Triggered Mobility (LTM) candidate configuration.

[0601] In various embodiments, the candidate configuration is an RRC configuration that includes or is associated with the configuration of the candidate cell.

[0602] Now return to reference Figure 3 and Figure 4 In one or more embodiments from the perspective of the UE, the apparatus 300 includes program code 312 stored in the memory 310 of the transmitter. The CPU 308 may execute the program code 312 to: (i) store or maintain the TA for the candidate cell; (ii) clear the TA of the candidate cell in response to at least one of the following: expiration of a timer; reconfiguration of a candidate configuration associated with the candidate cell; the UE entering the RRC_IDLE state or the RRC_INACTIVE state; and / or the UE switching its SpCell to a second candidate cell. In addition, the CPU 308 may execute the program code 312 to perform all described actions, steps, and methods described above, below, or otherwise herein.

[0603] See also Fig. 20 , with respect to such and other concepts, systems and methods of the present invention, a method 1010 for a UE in a wireless communication system includes transmitting a report to a network, wherein the report contains or indicates a TA storage status of one or more candidate cells (step 1012).

[0604] In various embodiments, the report is a MAC CE or an RRC message.

[0605] In various embodiments, the report indicates one or more IDs associated with the one or more candidate cells.

[0606] In various embodiments, the report indicates a bitmap indicating the one or more candidate cells.

[0607] In various embodiments, the report indicates whether the TA has been stored or a stored TA has been removed or cleared for the one or more candidate cells.

[0608] In various embodiments, the report indicates a TA value for the one or more candidate cells.

[0609] In various embodiments, the UE triggers transmission of the report in response to obtaining or clearing a stored TA for at least one candidate cell.

[0610] In various embodiments, the UE triggers transmission of the report in response to replacing a stored TA or updating a stored TA value for at least one candidate cell.

[0611] In various embodiments, the UE triggers transmission of the report in response to expiration of a timer.

[0612] In various embodiments, the UE triggers transmission of the report in response to receiving PDCCH signaling from the network.

[0613] In various embodiments, the UE triggers transmission of a report in response to invalidity of a stored TA associated with a candidate cell.

[0614] In various embodiments, the TA storage is a list (or set) of stored TAs for the one or more candidate cells.

[0615] In various embodiments, the PDCCH signaling is a PDCCH order.

[0616] In various embodiments, the candidate configuration is a L1 / L2 Triggered Mobility (LTM) candidate configuration.

[0617] In various embodiments, the candidate configuration is an RRC configuration that includes or is associated with the configuration of the candidate cell.

[0618] Now return to reference Figure 3 and Figure 4 In one or more embodiments from the perspective of the UE, the apparatus 300 includes program code 312 stored in a memory 310 of the transmitter. The CPU 308 may execute the program code 312 to: (i) transmit a report to the network, wherein the report contains or indicates the TA storage status of one or more candidate cells. In addition, the CPU 308 may execute the program code 312 to perform all described actions, steps, and methods described above, below, or otherwise herein.

[0619] See also Fig.21 , with respect to such and other concepts, systems and methods of the present invention, a method 1020 for a UE in a wireless communication system includes receiving a configuration indicating at least one candidate cell including a first candidate cell (step 1022), storing a first TA associated with the first candidate cell (step 1024), and clearing or discarding the first TA associated with the first candidate cell in response to at least one of the following: expiration of a timer associated with the first TA; performing RRC re-establishment; the UE entering an RRC_IDLE state or an RRC_INACTIVE state; a serving cell change; and / or the UE storing a second TA when a list or set of stored TAs for the at least one candidate cell is full (step 1026).

[0620] In various embodiments, the UE obtains the first TA by receiving a message or signaling indicating the first TA.

[0621] In various embodiments, the UE obtains the first TA through UE-based TA measurement.

[0622] In various embodiments, the UE starts or restarts the timer in response to obtaining or updating the first TA.

[0623] In various embodiments, the serving cell change is performed in response to a reconfiguration or LTM procedure with synchronization.

[0624] In various embodiments, the UE, when initiating the LTM procedure to the second candidate cell, stores the third TA associated with the source (serving) cell (of the LTM procedure).

[0625] In various embodiments, the UE clears or discards the first TA based on an ID associated with the first TA, an ID associated with the first candidate cell, or a remaining valid time of the first TA.

[0626] In various embodiments, the UE clears or discards the first TA based on the following: the ID associated with the first TA is the lowest among the IDs of the stored (and / or valid) TAs associated with the at least one candidate cell, the ID associated with the first candidate cell is the lowest among the IDs of the at least one candidate cell with the stored (and / or valid) TA, the remaining valid time of the first TA is the shortest among the at least one candidate cell with the stored (and / or valid) TA, the first TA is the first TA stored in the list or set of stored TAs, or the first TA is invalid.

[0627] Now return to reference Figure 3 and Figure 4In one or more embodiments from the perspective of the UE, the apparatus 300 includes program code 312 stored in a memory 310 of the transmitter. The CPU 308 may execute the program code 312 to: (i) receive a configuration indicating at least one candidate cell including a first candidate cell; (ii) store a first TA associated with the first candidate cell; and (iii) clear or discard the first TA associated with the first candidate cell in response to at least one of the following: expiration of a timer associated with the first TA; performing RRC re-establishment; the UE entering an RRC_IDLE state or an RRC_INACTIVE state; a serving cell change; and / or the UE storing a second TA when the list or set of stored TAs for the at least one candidate cell is full. In addition, the CPU 308 may execute the program code 312 to perform all of the described actions, steps, and methods described above, below, or otherwise herein.

[0628] See also Fig. 22 , with respect to such and other concepts, systems and methods of the present invention, a method 1030 for a UE in a wireless communication system includes receiving a configuration indicating at least one candidate cell including a first candidate cell (step 1032), storing a first TA associated with the first candidate cell (step 1034), and transmitting a report to a network, wherein the report indicates information related to the first TA (step 1036).

[0629] In various embodiments, the UE transmits the report in response to a change in the list or set of stored TAs for the at least one candidate cell or in response to signaling indicated by the network.

[0630] In various embodiments, the information indicates at least one of: a candidate cell having a stored (and / or valid) TA, a first TA, the number of stored (and / or valid) TAs for the at least one candidate cell, or the maximum number of stored TAs for the at least one candidate cell.

[0631] In various embodiments, the information comprises at least one of: a bitmap indicating candidate configurations associated with the at least one candidate cell and having a stored and / or valid TA, or a bit indicating whether the first candidate cell has a stored (and / or valid) TA (or not).

[0632] In various embodiments, the UE transmits the maximum number of stored TAs for the at least one candidate cell via a message different from the report.

[0633] In various embodiments, the UE obtains the first TA by receiving a message or signaling indicating the first TA.

[0634] In various embodiments, the UE obtains the first TA through UE-based TA measurement.

[0635] Now return to reference Figure 3 and Figure 4 In one or more embodiments from the perspective of the UE, the apparatus 300 includes program code 312 stored in a memory 310 of the transmitter. The CPU 308 may execute the program code 312 to: (i) receive a configuration indicating at least one candidate cell including a first candidate cell; (ii) store a first TA associated with the first candidate cell; and (iii) transmit a report to the network, wherein the report indicates information related to the first TA. In addition, the CPU 308 may execute the program code 312 to perform all described actions, steps, and methods described above, below, or otherwise herein.

[0636] Any combination of the concepts or teachings above or herein may be fully or partially combined or formed into new embodiments. The disclosed details and embodiments may be used to at least (but not limited to) solve the problems mentioned above and herein.

[0637] It should be noted that any of the methods, alternatives, steps, examples and embodiments presented herein may be applied independently, individually and / or in combination with multiple methods, alternatives, steps, examples and embodiments.

[0638] Various aspects of the present disclosure have been described above. It should be clear that the teachings herein can be implemented in a wide variety of forms, and any specific structure, function, or both disclosed herein are only representative. Based on the teachings herein, it should be understood by those skilled in the art that the aspects disclosed herein can be implemented independently of any other aspects, and two or more of these aspects can be combined in different ways. For example, any number of aspects set forth herein can be used to implement a device or practice method. In addition, by using other structures, functionality, or structures and functionality other than one or more aspects of the aspects set forth herein or different from one or more aspects of the aspects set forth herein, this device can be implemented or this method can be practiced. As an example of some of the above concepts, in some aspects, parallel channels can be established based on pulse repetition frequencies. In some aspects, parallel channels can be established based on pulse positions or offsets. In some aspects, parallel channels can be established based on time hopping sequences. In some aspects, parallel channels can be established based on pulse repetition frequencies, pulse positions or offsets, and time hopping sequences.

[0639] Those skilled in the art will appreciate that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0640] Those of ordinary skill in the art will further appreciate that the various illustrative logical blocks, modules, processors, components, circuits, and algorithm steps described in conjunction with the various aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which may be designed using source decoding or some other technique), and various forms of programs or design code with instructions (which may be referred to herein as "software" or "software modules" for convenience), or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

[0641] In addition, the various illustrative logical blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented within or performed by an integrated circuit ("IC"), an access terminal, or an access point. The IC may include a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute code or instructions residing within the IC, outside the IC, or both. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0642] It should be understood that any specific order or hierarchy of steps in any disclosed process is an example of an exemplary method. It should be understood that based on design preferences, the specific order or hierarchy of steps in a process can be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order and are not intended to be limited to the specific order or hierarchy presented.

[0643] The steps of the method or algorithm described in conjunction with the various aspects disclosed herein can be implemented directly with hardware, with a software module executed by a processor, or with a combination of the two. Software modules (e.g., including executable instructions and related data) and other data can reside in a data memory, such as a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of a computer-readable storage medium known in the art. An example storage medium can be coupled to a machine such as a computer / processor (for convenience, the machine can be referred to as a "processor" in this article) so that the processor can read information (e.g., code) from a storage medium and write information to a storage medium. An example storage medium can be integrated with a processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a user device. In an alternative, the processor and storage medium can reside in a user device as discrete components. In addition, in some aspects, any suitable computer program product may include a computer-readable medium, which includes a code related to one or more of the various aspects of the present disclosure. In some aspects, a computer program product may include packaging materials.

[0644] Although the present invention has been described in conjunction with various aspects and examples, it will be appreciated that the present invention is capable of further modifications. This application is intended to cover any changes, uses or adaptations of the present invention, which generally follow the principles of the present invention and include such deviations from the present disclosure, which are within the scope of known and customary practice in the technical field to which the present invention belongs.

Claims

1. A method for handling a user equipment of a cell timing advance, characterized in that: include: receiving a configuration indicating at least one candidate cell including a first candidate cell; storing a first timing advance associated with the first candidate cell; as well as clearing or discarding the first timing advance associated with the first candidate cell in response to at least one of: expiration of a timer associated with the first timing advance; performing radio resource control re-establishment; The user equipment enters the RRC_IDLE state or the RRC_INACTIVE state; Service area changes; or The user equipment stores a second timing advance when the list or set of stored timing advances for the at least one candidate cell is full.

2. The method according to claim 1, characterized in that The user equipment obtains the first timing advance by receiving a message or signaling indicating the first timing advance or by timing advance measurement based on the user equipment.

3. The method according to claim 1, characterized in that The user equipment starts or restarts the timer in response to obtaining or updating the first timing advance.

4. The method according to claim 1, characterized in that: The serving cell change is performed in response to a mobility procedure with synchronized reconfiguration or L1 or L2 triggering.

5. The method according to claim 1, characterized in that The user equipment stores a third timing advance associated with the source cell when initiating an L1 or L2 triggered mobility procedure to a second candidate cell.

6. The method according to claim 1, characterized in that The user equipment clears or discards the first timing advance based on an identity associated with the first timing advance, an identity associated with the first candidate cell, or a remaining validity time of the first timing advance.

7. The method according to claim 1, characterized in that The user equipment clears or discards the first timing advance based on the following items: the identity associated with the first timing advance is the lowest among the identities of the stored or valid timing advances associated with the at least one candidate cell, the identity associated with the first candidate cell is the lowest among the identities of the at least one candidate cell with stored or valid timing advances, the remaining effective time of the first timing advance is the shortest among the at least one candidate cell with stored or valid timing advances, the first timing advance is the first timing advance stored in the list or the set of stored timing advances, or the first timing advance is invalid.

8. A method for handling a user equipment of a cell timing advance, characterized in that: include: receiving a configuration indicating at least one candidate cell including a first candidate cell; storing a first timing advance associated with the first candidate cell; as well as A report is transmitted to a network, wherein the report indicates information related to the first timing advance.

9. The method according to claim 8, characterized in that The user equipment transmits the report in response to a change in the list or set of stored timing advances for the at least one candidate cell or in response to signaling indicated by the network.

10. The method according to claim 8, characterized in that The information indicates at least one of: a candidate cell having a stored or valid timing advance, the first timing advance, a number of stored or valid timing advances for the at least one candidate cell, or a maximum number of stored timing advances for the at least one candidate cell.

11. The method according to claim 8, characterized in that The information comprises at least one of: a bitmap indicating candidate configurations associated with the at least one candidate cell and having a stored or valid timing advance, or a bit indicating whether the first candidate cell has a stored or valid timing advance.

12. The method according to claim 8, characterized in that The user equipment transmits the maximum number of stored timing advances for the at least one candidate cell via a message different from the report.

13. The method according to claim 8, characterized in that The user equipment obtains the first timing advance by receiving a message or signaling indicating the first timing advance or by timing advance measurement based on the user equipment.

14. A user equipment for handling timing advance of a cell, characterized in that: include: Memory; as well as a processor operatively coupled to the memory, wherein the processor is configured to execute program code to: receiving a configuration indicating at least one candidate cell including a first candidate cell; storing a first timing advance associated with the first candidate cell; and clearing or discarding the first timing advance associated with the first candidate cell in response to at least one of: expiration of a timer associated with the first timing advance; performing radio resource control re-establishment; The user equipment enters the RRC_IDLE state or the RRC_INACTIVE state; Service area changes; or The user equipment stores a second timing advance when the list or set of stored timing advances for the at least one candidate cell is full.

15. The user equipment according to claim 14, characterized in that: The user equipment obtains the first timing advance by receiving a message or signaling indicating the first timing advance or by timing advance measurement based on the user equipment.

16. The user equipment according to claim 14, characterized in that The user equipment starts or restarts the timer in response to obtaining or updating the first timing advance.

17. The user equipment according to claim 14, characterized in that: The serving cell change is performed in response to a mobility procedure with synchronized reconfiguration or L1 or L2 triggering.

18. The user equipment according to claim 14, characterized in that The user equipment stores a third timing advance associated with the source cell when initiating an L1 or L2 triggered mobility procedure to a second candidate cell.

19. The user equipment according to claim 14, characterized in that The user equipment clears or discards the first timing advance based on an identity associated with the first timing advance, an identity associated with the first candidate cell, or a remaining validity time of the first timing advance.

20. The user equipment according to claim 14, characterized in that The user equipment clears or discards the first timing advance based on the following items: the identity associated with the first timing advance is the lowest among the identities of the stored or valid timing advances associated with the at least one candidate cell, the identity associated with the first candidate cell is the lowest among the identities of the at least one candidate cell with stored or valid timing advances, the remaining effective time of the first timing advance is the shortest among the at least one candidate cell with stored or valid timing advances, the first timing advance is the first timing advance stored in the list or the set of stored timing advances, or the first timing advance is invalid.

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