Terminal device and method

Abstract

An exemplary embodiment of this disclosure relates to a solution for initiating a random access (RA) procedure. In this solution, a terminal device receives a first physical downlink control channel (PDCCH) order from a first network device to trigger a random access (RA) procedure for L1 / L2 triggered mobility (LTM). The first PDCCH order indicates a first RA resource. The terminal device determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover. The terminal device is being serviced in the first cell. If the first PDCCH order indicates a second cell, the terminal device ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource. The second RA resource is configured for the terminal device by the second network device.

Description

Technical Field

[0001] Exemplary embodiments of the present disclosure generally relate to the field of communication technologies, and particularly to methods, apparatuses, and media for initiating random access (RA) procedures.

Background Art

[0002] Communication systems have been widely introduced to provide various telecommunication services. For example, the mobility of devices within a communication network has been supported. The mobility function of a communication network can provide continuous coverage for a device when the device moves from one cell to another cell (also called inter-cell). For example, when a terminal device moves within a communication network, handover or cell switching may occur during the movement. It has been proposed to support layer 1 (L1) or layer 2 (L2) based inter-cell mobility for handover or cell switching, or L1 / L2 trigger mobility (LTM). Research on initiating RA procedures for LTM is in progress.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Generally, embodiments of the present disclosure provide a method, an apparatus, and a computer storage medium for initiating an RA procedure.

Means for Solving the Problems

[0004] In a first embodiment, a communication method is provided that is performed by a terminal device. This method includes receiving a first physical downlink control channel (PDCCH) order from a first network device that triggers a random access (RA) procedure, wherein the first PDCCH order indicates a first RA resource, and determining whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device is serviced in the first cell and, in response to the determination that the first PDCCH order indicates a second cell, ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource, wherein the second RA resource is configured for the terminal device by the second network device.

[0005] In a second embodiment, a communication method is provided which is performed by a second network device. This method includes setting up a second random access (RA) resource for a terminal device, the terminal device being served in a first cell of a first network device, the second RA resource including a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to a second cell of the second network device, and after the terminal device has switched from the first cell to the second cell, performing further RA procedures with the terminal device using the second RA resource, and sending further RARs to the terminal device for further RA procedures, regardless of whether the terminal device is configured to monitor RA Responses (RARs), the further RARs indicating at least TA information for the second cell.

[0006] In a third embodiment, a terminal device is provided comprising a processor, the processor receiving a first physical downlink control channel (PDCCH) order from a first network device for triggering a random access (RA) procedure, wherein the first PDCCH order indicates a first RA resource, and the processor determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device is serviced in the first cell and, in response to the determination that the first PDCCH order indicates a second cell, ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource, wherein the second RA resource is configured to be set up for the terminal device by the second network device.

[0007] In a fourth embodiment, a second network device is provided, comprising a processor, the processor configuring the second network device for a second random access (RA) resource for a terminal device, the terminal device being served in a first cell of the first network device, the second RA resource including a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to the second cell, and after the terminal device switches from the first cell to the second cell, the processor uses the second RA resource to perform further RA procedures with the terminal device, and sends further RARs to the terminal device for further RA procedures, regardless of whether the terminal device is configured to monitor RA responses (RARs), the further RARs are configured to indicate at least TA information for the second cell.

[0008] In a fifth embodiment, a computer-readable medium is provided which, when executed on at least one processor, stores instructions causing at least one processor to perform the method described in the first or second embodiment.

[0009] Other features of this disclosure can be easily understood through the following description. [Brief explanation of the drawing]

[0010] The above and other purposes, features, and advantages of this disclosure will become more apparent through a more detailed description of some exemplary embodiments of this disclosure in the accompanying drawings.

[0011] [Figure 1] This document illustrates an exemplary communication environment in which exemplary embodiments of this disclosure may be implemented.

[0012] [Figure 2] The following are signaling flows for initiating an RA procedure according to some exemplary embodiments of this disclosure.

[0013] [Figure 3] The processes for initiating an RA procedure according to some exemplary embodiments of this disclosure are shown.

[0014] [Figure 4] The following are some exemplary embodiments of the present disclosure of signaling flows for random access channel (RACH) initiation and RAR monitoring.

[0015] [Figure 5] The following are signaling flows for RA procedures without RAR monitoring, according to some exemplary embodiments of this disclosure.

[0016] [Figure 6] The present disclosure shows a process for an RA procedure according to some exemplary embodiments.

[0017] [Figure 7A] Figure 7A shows an illustrative diagram illustrating the timing of retransmission according to some exemplary embodiments of the present disclosure. [Figure 7B] Figure 7B shows an illustrative diagram illustrating the timing of retransmission according to some exemplary embodiments of the present disclosure.

[0018] [Figure 8A] Shows a process for RA resource selection procedures according to some exemplary embodiments of the present disclosure.

[0019] [Figure 8B] Shows another process for RA procedures without RAR monitoring according to some exemplary embodiments of the present disclosure.

[0020] [Figure 9A] Shows a process for monitoring RAR with RNTI according to some exemplary embodiments of the present disclosure.

[0021] [Figure 9B] Shows another process for monitoring RAR with RNTI according to some exemplary embodiments of the present disclosure.

[0022] [Figure 10] Shows a signaling flow for RA preamble retransmission according to some exemplary embodiments of the present disclosure.

[0023] [Figure 11] Shows a flowchart of a method implemented in a terminal device according to some exemplary embodiments of the present disclosure.

[0024] [Figure 12] Shows another flowchart of a method implemented in a network device according to some exemplary embodiments of the present disclosure.

[0025] [Figure 13] Shows a simplified block diagram of a device suitable for implementing exemplary embodiments of the present disclosure.

[0026] Throughout the drawings, the same or similar reference numerals represent the same or similar elements.

Mode for Carrying Out the Invention

[0027] Next, the principles of this disclosure will be described with reference to several exemplary embodiments. These embodiments are provided for illustrative purposes only and are intended to help those skilled in the art understand and implement this disclosure, and should not be considered to imply any limitation on the scope of this disclosure. The embodiments described herein may be implemented in various other ways than those described below.

[0028] In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as they would be generally understood by an ordinary person skilled in the art to which this disclosure belongs.

[0029] As used herein, the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of terminal devices include user equipment (UE), personal computers, desktops, mobile phones, cell phones, smartphones, personal digital assistants (PDA), portable computers, tablets, wearable devices, IoT (Internet of Things) devices, URLLC (Ultra-reliable and Low Latency Communication) devices, IoE (Internet of Everything) devices, machine type communication (MTC) devices, in-vehicle devices for V2X communication (X stands for pedestrian, vehicle, or infrastructure / network), IAB (Integrated Access and Backhaul) devices, spacecraft or aircraft in non-terrestrial networks (NTN) with satellites, including HAP (High Altitude Platform) and Unmanned Aircraft Systems (UAS), and various types of reality including augmented reality (AR), mixed reality (MR), and virtual reality (VR), as well as XR (eXtended). This includes, but is not limited to, image capture devices such as Reality devices, unmanned aerial vehicles (UAVs) that do not carry human pilots and are commonly known as drones, devices on high-speed trains (HSTs), digital cameras, sensors, game devices, music storage and playback devices, or internet devices that enable wireless or wired internet access or browsing.A “terminal device” further possesses “multicast / broadcast” capabilities and can support public safety, mission-critical, V2X applications, transparent IPv4 / IPv6 multicast distribution, IPTV, smart TV, wireless services, wireless software distribution, group communications, and IoT applications. It can also incorporate one or more Subscriber Identity Modules (SIMs), known as multi-SIMs. The term “terminal device” can be used interchangeably with UE, mobile station, subscriber station, mobile terminal, user terminal, or wireless device.

[0030] The term "network device" refers to a device that can provide or host a cell or coverage from which terminal devices can communicate. Examples of network devices include, but are not limited to, Node B (NodeB or NB), Evolutionary Node B (eNodeB or eNB), Next Generation Node B (gNB), Transmission Reception Point (TRP), Remote Radio Unit (RRU), Radio Head (RH), Remote Radio Head (RRH), IAB node, femtonode, piconode and other low-power nodes, and Reconfigurable Intelligent Surface (RIS).

[0031] Terminal devices or network devices may have artificial intelligence (AI) or machine learning capabilities. Generally, this includes models trained from a large amount of collected data for a specific function and can be used to predict some kind of information.

[0032] Terminal or network devices may operate in frequency bands such as FR1 (e.g., 450MHz to 6000MHz), FR2 (e.g., 24.25GHz to 52.6GHz), above 100GHz, or in terahertz (THz). Furthermore, they can operate in licensed / unlicensed / shared frequency bands. In MR-DC (Multi-Radio Dual Connectivity) application scenarios, terminal devices may have more than one connection to network devices. Terminal or network devices can operate in full-duplex, flexible-duplex, and cross-division-duplex modes.

[0033] Embodiments of the present disclosure may be implemented in test equipment, such as a signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, or channel emulator. In some embodiments, the terminal device may be connected to a first network device and a second network device. One of the first and second network devices may be a master node and the other a secondary node. The first and second network devices may use different radio access technologies (RATs). In some embodiments, the first network device may be a first RAT device and the second network device may be a second RAT device. In some embodiments, the first RAT device may be an eNB and the second RAT device may be a gNB. Information regarding different RATs may be transmitted from at least one of the first or second network device to the terminal device. In some embodiments, the first information may be transmitted from the first network device to the terminal device, and the second information may be transmitted from the second network device directly or via the first network device to the terminal device. In some embodiments, information regarding the configuration of a terminal device set by the second network device may be transmitted from the second network device via the first network device. Information regarding the reconfiguration of a terminal device set by the second network device may be transmitted from the second network device directly to the terminal device or via the first network device.

[0034] Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context clearly indicates otherwise. The term “including” and its variations are read as an open term meaning “including, but not limited to.” The term “based on” is read as “based at least partially.” The terms “one embodiment” and “embodiment” are read as “at least one embodiment.” The term “another embodiment” is read as “at least one other embodiment.” Terms such as “first,” “second,” etc., may refer to different or the same subject. Other explicit and implicit definitions may be included below.

[0035] In some examples, values, procedures, or devices are referred to as “best,” “lowest,” “highest,” “minimum,” “maximum,” etc. Such descriptions are intended to indicate that a choice can be made from among many usable functional options, and it should be understood that such a choice does not necessarily have to be superior, smaller, higher, or otherwise preferable to other choices.

[0036] As used herein, the terms “resource,” “transmit resource,” “uplink resource,” or “downlink resource” may refer to any resource for performing communication, such as resources in the time domain, resources in the frequency domain, resources in the spatial domain, resources in the code domain, or other resources that enable communication. Hereinafter, unless otherwise specified, resources in both the frequency domain and the time domain will be used as examples of transmit resources to describe some exemplary embodiments of this disclosure. It should be noted that the exemplary embodiments of this disclosure are equally applicable to other resources in other domains.

[0037] As mentioned above, communication network mobility allows for continuous coverage to be provided to devices, such as terminal devices, when they move from one cell to another (also known as inter-cell communication). For example, when a terminal device moves within a communication network, a handover or cell switching may occur during the move. Layer 3 (L3) mobility has been proposed in several mechanisms for managing inter-cell mobility, such as handover management. However, such L3-based mobility may result in delays or communication interruptions when terminal devices move from one cell to another.

[0038] In some mechanisms, L1 / L2-based inter-cell mobility, also known as LTM, has been proposed to support inter-cell mobility for handover or cell switching. LTM can be applied to reduce mobility delay. For example, centralized unit (CU) / distributed unit (DU) interface signaling is used to support L1 / L2 mobility. Further discussion and improvement are needed regarding L1 / L2-based inter-cell mobility or LTM. Examples of communication environments

[0039] Figure 1 shows a schematic diagram of an exemplary communication environment 100 in which exemplary embodiments of the present disclosure may be implemented. In the communication environment 100, multiple communication devices, including a terminal device 110, a network device 120-1, a network device 130-2, ..., a network device 120-N, can communicate with each other. The network devices 120-1, 130-2, ..., a network device 120-N may be collectively referred to as "network device(s) 120" or individually as "network device 120". The numerical value N may be any appropriate integer value.

[0040] In the example in Figure 1, terminal device 110 may be a UE, and network device 120 may be a base station providing services to the UE. The serving area of ​​network device 120 may be called cell 122. For example, the serving area of ​​network device 120-1 is cell 122-1, the serving area of ​​network device 120-2 is cell 122-2, and the serving area of ​​network device 120-N is cell 122-N. Cells 122-1, 122-2, ..., and 122-N may be collectively referred to as "cell(plural) 122" or individually as "cell 122".

[0041] As shown in the figure, terminal device 120 is currently being serviced by cell 122-1 of network device 120-1. In this case, cell 122-1 may be called the serving cell or the first cell, and network device 120-1 may be called the service network device or the first network device. In a handover scenario, cell 122-2 or cell 122-N may be called the candidate cell or second cell for handover, and network device 120-2 or network device 120-N may be called the candidate network device or the second network device.

[0042] In some exemplary embodiments, terminal device 110 may move to another cell. For example, if terminal device 110 moves to cell 122-2 of network device 120-2, a handover or cell switchover may occur. After the handover, cell 122-2 may become the serving cell, and cell 122-1 may become a candidate cell. It should be understood that, depending on the situation, either cell can become the serving cell or a candidate cell.

[0043] In the communication environment 100, the network device 120 and the terminal device 110 can communicate data and control information with each other. The terminal devices 110 can also communicate with each other.

[0044] Please understand that the number of devices and their connections shown in Figure 1 are for illustrative purposes only and do not imply any limitations. The communication environment 100 may include any appropriate number of devices configured to carry out exemplary embodiments of this disclosure. Please understand that one or more additional devices may be located within a cell, and one or more additional cells may be deployed within the communication environment 100, although these are not shown. Please note that while the network device 120 is shown as a network device, it may be a device other than a network device. While the terminal device 110 is shown as a terminal device, it may be a device other than a terminal device.

[0045] For the sake of clarity, several exemplary embodiments will be described below in which the terminal device 110 operates as a UE and the network device 120 operates as a base station. However, in some exemplary embodiments, the operations described with respect to the terminal device may be performed by the network device or other devices, and the operations described with respect to the network device may be performed by the terminal device or other devices.

[0046] In some exemplary embodiments, when terminal device 110 is a terminal device and network device 120 is a network device, the link from network device 120 to terminal device 110 is called a downlink (DL), and the link from terminal device 110 to network device 120 is called an uplink (UL). In a DL, network device 120 is a transmitting (TX) device (or transmitter), and terminal device 110 is a receiving (RX) device (or receiver). In a UL, terminal device 110 is a TX device (or transmitter), and network device 120 is an RX device (or receiver).

[0047] Communication in the communication environment 100 includes, but is not limited to, GSM (Global System for Mobile Communications), LTE (Long Term Evolution), LTE-Evolution, LTE-Advanced (LTE-A), NR (New Radio), WCDMA (Wideband Code Division Multiple Access), CDMA (Code Division Multiple Access), GERAN (GSM EDGE Radio Access Network), MTC (Machine Type Communication), and any other suitable standard. Embodiments of this disclosure may be implemented in accordance with any generation of communication protocol that is currently known or will be developed in the future. Examples of communication protocols include, but are not limited to, first-generation (1G), second-generation (2G), 2.5G, 2.75G, third-generation (3G), fourth-generation (4G), 4.5G, fifth-generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or sixth-generation (6G) networks.

[0048] The principles and implementation of this disclosure are described in detail below with reference to the drawings.

[0049] Example of RA procedure initiation To address at least some of the above-mentioned problems or other potential problems, a solution relating to RA procedure initiation is proposed. According to embodiments of this disclosure, a terminal device receives a first physical downlink control channel (PDCCH) order from a first network device to trigger a random access (RA) procedure for L1 / L2 triggered mobility (LTM). The first PDCCH order indicates a first RA resource. The terminal device determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover. The terminal device is being serviced in the first cell. If the first PDCCH order indicates a second cell, the terminal device ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource. The second RA resource is configured for the terminal device by the second network device.

[0050] In this way, the terminal device can decide whether to initiate an RA procedure toward the serving cell from which it is receiving service, or to initiate an RA procedure toward a candidate cell based on a PDCCH order. Such a simplified decision process can contribute to reducing mobility delays.

[0051] In some cases, while terminal device 110 is being serviced by a cell (referred to as the “first cell”), it may receive a PDCCH order from the serving network device indicating a cell for initiating an RA procedure. Figure 2 shows a signaling flow 200 for initiating an RA procedure according to some exemplary embodiments of this disclosure. As shown in Figure 2, the signaling flow 200 involves terminal device 110, network device 120-1, and network device 120-2 in Figure 1. The illustrated signaling flow 200 assumes that terminal device 110 is currently being serviced by cell 122-1 of network device 120-1 (also referred to as the “first cell” or “serving cell”). Cell 122-2 of network device 120-2 (also referred to as the “second cell”, “candidate cell”, or “target cell”) is the cell for handover. As used herein, network device 120-1 may be referred to as the “first network device,” and network device 120-2 may be referred to as the “second network device.” The signaling flow 200 may involve more or fewer devices, and the number of devices shown in Figure 2 is for illustrative purposes only and does not imply any limitation.

[0052] In operation, network device 120-1 sends a first PDCCH order to terminal device 110 (210) to trigger an RA procedure. The first PDCCH order initiates a first RA resource. The PDCCH order may be a medium access control (MAC) entity. For example, the first RA resource contains downlink control information (DCI) format 1_0 for the RA procedure indicated by the PDCCH order.

[0053] In some embodiments, the RA procedure may be initiated by a first PDCCH order, the MAC entity itself, or an RRC for an event. In a MAC entity, one RA procedure is in progress at any given time. The RA procedure on the SCell is initiated by a PDCCH order having a different ra-PreambleIndex than 0b000000.

[0054] If a new RA procedure is triggered while another RA procedure is already in progress within the MAC entity, it is up to the implementation of the terminal device 110 to decide whether to continue the ongoing procedure or to start the new procedure (e.g., a system information (SI) request).

[0055] If there is an ongoing RA procedure triggered by a PDCCH order, but terminal device 110 receives another PDCCH order indicating the same RA preamble, physical random access channel (PRACH) mask index, and uplink carrier, that RA procedure is considered the same as the ongoing one and is not reinitialized.

[0056] In some embodiments, the cyclic redundancy check (CPC) of DCI format 1_0 is scrambled by a cell-radio network temporary identifier (C-RNTI), the "Frequency Domain Resource Allocation" field is all 1, DCI format 1_0 is for RA procedures initiated by a first PDCCH order, and the remaining fields are all set as shown in Table 1. [Table 1]

[0057] The exemplary structure or fields of the RA resources described above are for illustrative purposes only and do not imply any limitations. Any suitable RA resource is applicable. The scope of this disclosure is not limited in this respect.

[0058] Terminal device 110 receives a first PDCCH order (220). Terminal device 110 determines whether the first PDCCH order indicates a first cell of network device 120-1 (e.g., cell 122-1) or a second cell of network device 120-2 for handover (e.g., cell 122-2) (230).

[0059] If the first PDCCH order indicates a first cell such as cell 122-1, the terminal device 110 uses the first RA resource in the first PDCCH order to initiate an RA procedure toward the network device 120-1 (245). For example, if the candidate cell indication field in DCI format 1_0 indicated in the first PDCCH order indicates cell 122-1, the terminal device 110 uses the first RA resource in the first PDCCH order to initiate an RA procedure toward the network device 120-1.

[0060] For example, if the "Random Access Preamble Index" is not entirely zero and is set, and the Candidate Cell Indicator field points to cell 122-1, the SS / PBCH index field (e.g., 6 bits) indicates the SS / PBCH to be used to determine the RACH opportunity for PRACH transmission. Otherwise, this field is reserved.

[0061] In another example, if ra-PreambleIndex is not 0b000000 and is set, and the candidate cell indicator field points to cell 122-1, then PREAMBLE_INDEX is set to the signaled ra-PreambleIndex, and the SSB signaled by PDCCH is selected. This process is defined in Table 2 below. [Table 2]

[0062] If the first PDCCH order points to cell 122-2, the terminal device ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward cell 122-2 using the second RA resource (240). The second RA resource is set by the network device 120-2 for the terminal device 110. In some embodiments, an RA procedure in a secondary cell (SCell) such as cell 122-2 may be initiated by a PDCCH order having a different ra-PreambleIndex than 0b000000.

[0063] For example, if the candidate cell instruction field of DCI format 1_0 indicated in the first PDCCH order includes an instruction for cell 122-2, the terminal device uses a second RA resource to initiate an RA procedure toward cell 122-2 (240). For example, the second RA resource includes a contention-free RA (CFRA) resource.

[0064] In some exemplary embodiments, the second RA resource is a RACH resource configured by radio resource control (RRC) signaling. For example, terminal device 110 may be configured by an RRC RACH resource for each candidate cell, including cell 122-2. The configured RRC RACH resource may include at least an RA preamble index and an instruction for a RACH opportunity having an associated synchronization signal block (SSB) index for each candidate cell.

[0065] In some exemplary embodiments, if the candidate cell indicator field in the first RA resource does not indicate cell 122-1, or if the candidate cell indicator field indicates cell 122-2, at least one of the fields in the PDCH order of the RA preamble index, UL / SUL indicator, SS / PBCH index (e.g., 6 bits), or PRACH mask index may be ignored or reserved.

[0066] By initiating the RA procedure based on the cell indicated in the PDCCH order, source cells such as cell 122-1 no longer need to be aware of the RACH resources set by target cells such as cell 122-2 and reserved for terminal device 110 for CFRA within cell 122-2. The source cell can set any value in the field, and terminal device 110 can initiate CFRA based on the RRC setting by the target cell.

[0067] An exemplary embodiment of RA procedure initiation has been described with reference to Figure 2. By utilizing this RA procedure initiation, a terminal device may execute the RA procedure by selecting to use either a PDCCH order resource or an RRC configuration resource based on a PDCCH order. Such RA procedure initiation can contribute to reducing mobility delay. Further exemplary embodiments of RA procedure initiation will be described with reference to Figure 3.

[0068] Figure 3 shows a process 300 for initiating an RA procedure according to some exemplary embodiments of the present disclosure. For convenience of explanation, process 300 is described in terms of terminal device 110 in Figure 1. In the illustrated process 300, it is assumed that terminal device 110 is currently being serviced in cell 122-1 of network device 120-1 (also referred to as the “first cell” or “serving cell”). Cell 122-2 of network device 120-2 (also referred to as the “second cell” or “candidate cell” or “target cell”) is the cell for handover. As used herein, network device 120-1 may be referred to as the “first network device” and network device 120-2 may be referred to as the “second network device”.

[0069] In block 310, terminal device 110 determines whether the first PDCCH order indicates a first cell (e.g., cell 122-1) or a second cell (e.g., cell 122-2). If the first PDCCH order indicates a first cell, in block 350, terminal device 110 initiates an RA procedure toward network device 120-1 using the first RA resource.

[0070] If the first PDCCH order indicates the second cell, in block 320, the terminal device 110 may determine whether at least one of the multiple candidate synchronization signal blocks (SSBs) associated with the RA opportunity has a signal quality exceeding a first quality threshold. For example, the first quality threshold can be predefined or configurable. For instance, the first quality threshold can be set as rsrp-ThresholdSSB.

[0071] In some embodiments, L1 enhancements are applied for inter-cell beam management, such as L1 measurement and reporting and beam indication. Signal quality may be RSRP from L1 measurement.

[0072] If at least one SSB has a signal quality exceeding the first quality threshold, in block 330, the terminal device 110 initiates the RA procedure using the CFRA resource based on at least one SSB. Alternatively, if none of the candidate SSBs have a signal quality exceeding the first quality threshold, in block 340, the terminal device 110 initiates the RA procedure using the CFRA resource based on at least one of the candidate SSBs. For example, the terminal device 110 may select any SSB from among the relevant SSBs. The terminal device 110 may set PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB. The above process can be illustrated in Table 3 below. [Table 3]

[0073] By comparing signal quality and initiating the RA procedure according to the process described above, collision-free RACH is performed for RACH transmissions of the first PDCCH order in the candidate cell, even if the reference signal received power (RSRP) does not exceed the first quality threshold. This RA initiation method does not involve collision-based RACH, unlike some mechanisms in which the terminal device does not initiate an RA procedure using CFRA resources based on at least one of the multiple candidate SSBs, but instead performs collision-based RACH. In this way, collision-based RACH is not performed, and RACH delay can be reduced.

[0074] Exemplary embodiments of RA procedure initiation have been described. By utilizing this RA procedure initiation, a terminal device can execute the RA procedure based on a PDCCH order, by selecting to use either a PDCCH order resource or an RRC configuration resource. Such RA procedure initiation can contribute to reducing mobility delays.

[0075] Example of RACH startup and RAR monitoring In some scenarios, a terminal device is currently being serviced by a serving cell (referred to as the first cell) of a first network device. The terminal device is configured by a second network device with an RRC having RACH resources such as those specified in Table 1. The terminal device may be instructed by a PDCCH order to initiate RACH in a candidate cell (referred to as the second cell) of the second network device. Embodiments of this disclosure propose solutions that improve RACH initiation and RAR monitoring.

[0076] In this solution, the second network device configures a second random access (RA) resource for the terminal device. The second RA resource includes a collision-free RA (CFRA) resource for the terminal device to initiate an RA procedure before it switches to the second cell of the second network device. After the terminal device switches from the first cell to the second cell, the second network device uses the second RA resource to perform further RA procedures with the terminal device. Regardless of whether the terminal device is configured to monitor RA responses (RARs), the network device sends further RARs to the terminal device for further RA procedures. These further RARs include at least timing advance (TA) information for the second cell.

[0077] In this way, the second network device can set or display TA information to the terminal device after the terminal device has switched to the second cell of the second network device. By displaying TA information, the handover delay for obtaining TA information for the second cell can be reduced, and TA management can be improved.

[0078] Figure 4 shows a signaling flow 400 for RACH initiation and RAR monitoring according to some exemplary embodiments of this disclosure. As shown in Figure 4, the signaling flow 400 involves terminal device 110 and network device 120-2 (referred to as the “second network device”) in Figure 1. Terminal device 110 is serviced in cell 122-1 (also referred to as the “first cell” or “serving cell”) of network device 120-1 (referred to as the “first network device”). Cell 122-2 (also referred to as the “second cell,” “candidate cell,” or “target cell”) of network device 120-2 is a cell for handover. The signaling flow 400 may involve more or fewer devices, and it should be understood that the number of devices shown in Figure 4 is for illustrative purposes only and does not imply any limitation.

[0079] In operation, network device 120-2 configures a second random access (RA) resource for terminal device 110. The second RA resource includes a CFRA resource for terminal device 110 to initiate an RA procedure before terminal device 110 switches to a second cell of network device 120-2 (e.g., cell 122-2). That is, terminal device 110 is configured with an RRC RACH resource that includes at least an RA preamble index and instructions for RACH opportunities with the associated SSB index for each candidate cell.

[0080] Terminal device 110 may be instructed by a PDCCH order to start RACH on a candidate cell such as cell 122-2. For example, terminal device 110 may receive a PDCCH order from network device 120-1 to start RACH on cell 122-2.

[0081] In some embodiments, terminal device 110 receives a handover command from, for example, network device 120-1. In some exemplary embodiments, RRC configuration measurements are performed in cells 122-1 and 122-2. Terminal device 110 performs the measurements and reports the results to the network. The RRC may indicate a handover command (an RRC reconfiguration message including reconfigurationWithSync IE) by indicating the target cell common configuration for cell 122-2, the non-collision RACH resources for cell 122-2 (preamble index, RACH opportunity, etc.), and the C-RNTI used for cell 122-2.

[0082] In response to the handover command, terminal device 110 performs the handover procedure from cell 122-1 to cell 122-2 (420). That is, terminal device 110 synchronizes with cell 122-2. For example, terminal device 110 may perform the following operations shown in Table 4 to perform a synchronized reset. [Table 4]

[0083] After the terminal device switches from cell 122-1 to cell 122-2, the terminal device 110 and the network device 120-2 may perform further RA procedures using a second RA resource (440). For example, the terminal device 110 sends a RACH preamble to the network device 120-2. After the cell switch, the terminal device should understand that it is served by cell 122-2 of the network device 120-2. Consequently, cell 122-1 of the network device 120-1 becomes a candidate cell.

[0084] In some exemplary embodiments, terminal device 110 determines whether the timing advance (TA) information for cell 122-2 is unavailable or invalid (430). In some embodiments, RAR reception may be set / instructed for a candidate cell(s) with a PDCCH order RACH. If RAR reception is not set / instructed (no RAR), the TA value of the candidate cell(s) may be indicated by a cell switching command or a handover command.

[0085] If the handover command does not include TA information, or if the handover command indicates an invalid TA value, the TA information is considered unavailable or invalid. If the RAR is deemed successful and the TA information or TA command is valid, the terminal device 110 may apply the TA command in the RAR and consider the RACH to have completed successfully. If the RACH is deemed to have completed successfully, the terminal device 110 may consider the handover to have completed.

[0086] If the TA information is unavailable or invalid, the terminal device 110 may use the CFRA resources to initiate further RA procedures toward cell 122-2.

[0087] In some exemplary embodiments, if terminal device 110 receives a handover command and is configured to monitor the RAR of cell 122-2, and the TA information is unavailable or invalid, terminal device 110 switches to cell 122-2 and does not need to perform any UL transmissions on cell 122-2 except for the RA preamble, because the timeAlignmentTimer to which cell 122-2 belongs is not operating.

[0088] Alternatively or additionally, if terminal device 110 is configured to receive a handover command and monitor the RAR in cell 122-2, and terminal device 110 does not receive the RAR in cell 122-2 to complete RACH, terminal device 110 may switch to cell 122-2 and, since the timeAlignmentTimer to which cell 122-2 belongs is not operating, may not perform any UL transmissions on cell 122-2 except for the RA preamble.

[0089] In some exemplary embodiments, network device 120-2 sends further RARs for further RA procedures to terminal device 110, regardless of whether terminal device 110 is configured to monitor RARs (450). The further RARs indicate at least TA information for cell 122-2. Terminal device 110 may monitor or receive further RARs for further RA procedures from network device 120-2, regardless of whether it is configured to monitor RARs (460). That is, terminal device 110 may start RACH on cell 122-2 using RACH resources configured for cell 122-2 and monitor RARs. Network device 120-2 may send RARs on cell 122-2, regardless of whether terminal device 110 is configured to monitor RARs (450). This gives terminal device 110 an opportunity to obtain TA information when terminal device 110 switches to cell 122-2 or is configured not to monitor RARs.

[0090] In this way, in situations where the channel state requires an immediate handover, if RACH is not successfully completed in a candidate cell such as cell 122-2, the terminal device 110 first switches to the candidate cell, and then reduces the delay by using CFRA RACH on the candidate cell.

[0091] In some embodiments, the TA field in the command that triggers cell switching may have a special value indicating invalid TA information. This is applicable to situations where a handover should be triggered, but the candidate cell has not detected RACH or TA information has not yet been received from the candidate cell.

[0092] In relation to Figure 4, exemplary embodiments of RACH initiation and RAR monitoring have been described. RACH initiation and RAR monitoring according to this disclosure can reduce mobility delays or handover delays.

[0093] Example of an RA procedure without RAR monitoring In some scenarios, after sending an RA preamble, the terminal device needs to monitor the RAR. Depending on the legacy RA mechanism, the terminal device may perform the actions shown in Table 5 below. [Table 5]

[0094] Through several legacy RA mechanisms, terminal devices may perform operations such as RACH power ramping, as shown in Table 6 below. [Table 6]

[0095] As mentioned above, according to some legacy mechanisms, terminal devices perform RAR monitoring during RA procedures. However, in some scenarios where RA procedures for candidate cells or non-serving cells are initiated based on PDCCH orders, RAR monitoring can cause delays. To address at least some of the above and other potential problems, several solutions for RA procedures without RAR monitoring have been proposed. These solutions are described with reference to Figures 5 to 7B.

[0096] In the following embodiments relating to Figures 5 to 7B, it is assumed that terminal device 110 is currently being serviced by cell 122-1 (referred to as the "first cell" or "serving cell") of network device 120-1 (referred to as the "first network device" or "serving network device"). Terminal device 110 receives a PDCCH order from network device 120-1 indicating the cell for initiating the RA procedure. Cell 122-2 (referred to as the "second cell," "candidate cell," or "target cell") of network device 120-2 (referred to as the "second network device") is the cell for handover.

[0097] Figure 5 shows a signaling flow 500 for performing an RA procedure without RAR monitoring, according to some exemplary embodiments of this disclosure. As shown in Figure 5, the signaling flow 500 involves terminal device 110 and network device 120-2 in Figure 1. The signaling flow 500 may involve more or fewer devices, and it should be understood that the number of devices shown in Figure 5 is for illustrative purposes only and does not imply any limitation.

[0098] In operation, terminal device 110 determines whether terminal device 110 is configured to monitor RAR for RA procedures (510). For example, terminal device 110 may determine whether to monitor RAR based on an RRC RACH resource or other appropriate signaling (510).

[0099] In some exemplary embodiments, if the terminal device 110 determines that it is not configured to monitor RAR for the RA procedure (510), the terminal device 110 determines that the RA procedure has completed successfully after it has started (540). That is, after performing a RACH preamble transmission to a target candidate cell such as cell 122-2, the terminal device 110 may consider the RA procedure to have completed successfully. In this way, the terminal device 110 can quickly complete the RACH procedure and return to the source cell, reducing downtime.

[0100] Alternatively or additionally, in some exemplary embodiments, if terminal device 110 is configured not to monitor RAR for an RA procedure, terminal device 110 determines (510) that the RA procedure has not completed successfully after it has started. Terminal device 110 may transmit an RA preamble to network device 120-2 a predetermined number of times during the RA procedure (520). Network device 120-2 may receive an RA preamble (or more) (530).

[0101] In some embodiments, after transmitting the RA preamble, the terminal device 110 may consider the RACH procedure incomplete because it does not receive a RAR. Alternatively, in some embodiments, the terminal device 110 may determine that the RA procedure has been successfully completed after the RA preamble has been transmitted a predetermined number of times (540). The predetermined number is configurable. For example, the predetermined number may be less than preambleTransMax. As another example, the predetermined number may be defined as the minimum value of preambleTransMax. In such cases, the terminal device 110 may further consider the power ramping step to be zero or not increment a power ramping counter such as PREAMBLE_POWER_RAMPING_COUNTER.

[0102] In this way, autonomous repetition can be achieved. The terminal device 110 may decide on the opportunity for the next preamble transmission after the previous preamble transmission. Figure 7A shows an illustrative figure 700 illustrating the retransmission timing in such a case. As shown, the terminal device 110 performs the initial transmission 710 at the RACH opportunity (RO) 702. If the initial transmission 710 is not completed after RO 702, the terminal device 110 may perform an autonomous retransmission 720 at RO 704. In this embodiment, since the RAR is not monitored, the terminal device 110 can perform an autonomous retransmission 720 at RO 704 without waiting for the search space (SS). Note that the number of ROs and SSs are for illustrative purposes only and do not imply any limitations.

[0103] Continuing to refer to Figure 5, in some exemplary embodiments, if the terminal device 110 determines (510) that it is configured to monitor RAR, the terminal device 110 may perform further actions. For example, the terminal device 110 may perform actions according to Table 5 above. When performing actions according to Table 5, the terminal device 110 may monitor RAR using a RAR timer such as ra-ResponseWindow configured in RACH-ConfigCommon.

[0104] Alternatively, in some embodiments, the terminal device 110 may perform process 600 for the RA procedure shown in Figure 6. For convenience of explanation, process 600 will be described in terms of the terminal device 110 in Figure 1.

[0105] In block 610, the terminal device 110 monitors the RAR for the RA procedure by setting the RA timer to zero. That is, the terminal device 110 monitors the RAR but considers the RA timer to be zero.

[0106] In block 620, the terminal device 110 determines whether the RAR timer has expired. If the RAR timer is set to zero in block 610, the terminal device 110 determines that the RAR timer has expired in block 620.

[0107] If the RAR timer expires, in block 630, the terminal device 110 determines that the RA preamble in the RA procedure was transmitted on a secondary cell (SCell) such as cell 122-2. The terminal device 110 considers the RACH transmission on the target candidate cell as a transmission on the SCell.

[0108] If the RA preamble is transmitted on a SCell such as cell 122-2, in block 640 the terminal device 110 may determine that the RA procedure has not been successfully completed. The terminal device 110 may further consider the power ramping step to be zero, or it may not increment a power ramping counter such as PREAMBLE_POWER_RAMPING_COUNTER.

[0109] In this way, autonomous repetition can be achieved. The terminal device 110 may determine the next opportunity for preamble transmission after the next opportunity following the expiration of the RAR. Figure 7B shows an example diagram 750 illustrating the retransmission timing in such a case. As shown, similar to Figure 7A, the terminal device 110 performs the initial transmission 710 at RACH opportunity (RO) 702. The difference from Figure 7A is that if the initial transmission 710 is not completed after RO 702, the terminal device 110 may perform autonomous retransmission 760 at RO 762 instead of RO 704. This is because the terminal device 110 is monitoring the RAR, which allows the terminal device 110 to perform autonomous retransmission 720 after SS. Note that the numbers of RO and SS are for illustrative purposes only and do not imply any limitations.

[0110] In process 600, RAR monitoring is performed, but because the RAR timer is set to zero, the RAR monitoring time is extremely short. An RA process with such a short RAR monitoring period can be considered an RA procedure without RAR monitoring.

[0111] Continuing to refer to Figure 5, in some exemplary embodiments, if it is determined that the terminal device 110 is configured not to monitor the RAR for the RA procedure (510), the terminal device 110 may decide to perform process 800 or process 860, which will be described in relation to Figures 8A and 8B, respectively (540).

[0112] Figure 8A shows a process 800 for performing an RA resource selection procedure according to some exemplary embodiments of the present disclosure. For convenience of explanation, the process 800 will be described in terms of the terminal device 110 in Figure 1.

[0113] In block 810, terminal device 110 determines that the RA procedure is not complete. For example, terminal device 110 may determine that the RA procedure is pending. In block 820, terminal device 110 may increment the retransmission counter in the RA preamble of the RA procedure. For example, terminal device 110 may increase the retransmission counter by 1.

[0114] In block 830, the terminal device 110 determines whether the RA procedure is incomplete (or not completed) and whether the retransmission counter is within the retransmission upper limit threshold. The retransmission upper limit threshold can be predefined or configurable. For example, the retransmission upper limit threshold may be preambleTransMax.

[0115] If the RA procedure is not complete and the retransmission counter is within the retransmission upper threshold, in block 840, the terminal device 110 determines whether it has received a second PDCCH order indicating a second cell, such as cell 122-2. If it has received a second PDCCH order indicating a second cell, in block 850, the terminal device 110 may perform the RA resource selection procedure.

[0116] In other words, the terminal device 110 does not need to perform the RA resource selection procedure until it receives a PDCCH order indicating the same candidate cell. In some embodiments, if the terminal device 110 receives a PDCCH order indicating the same candidate cell, such as cell 122-2, the terminal device 110 does not need to start a retransmission counter such as PREAMBLE_TRANSMISSION_COUNTER or a power ramping counter such as PREAMBLE_POWER_RAMPING_COUNTER.

[0117] In some embodiments, the terminal device 110 may reset a power ramping counter, such as PERAMBLE_POWER_RAMPING_COUNTER, after a set timer has expired or after a new RRC setting, MAC CE command, or instruction in the PDCCH order.

[0118] Figure 8B shows process 860 executed during an RA procedure without RAR monitoring. In some embodiments, if terminal device 110 is configured not to monitor RAR, terminal device 110 may execute process 860. For illustrative purposes, process 860 is described from the perspective of terminal device 110 in Figure 1.

[0119] In block 860, the terminal device 110 determines whether the SSB signal quality for initiating the RA procedure exceeds a second quality threshold. The second quality threshold is predefined or configurable. Signal quality may be synchronization signal based reference signal received power (SS-RSRP) or other signal quality parameters.

[0120] If the SSB signal quality exceeds the second quality threshold, in block 890, the terminal device 110 may determine that the RA procedure has been successfully completed. For example, the terminal device 110 does not need to perform autonomous retransmission.

[0121] Alternatively, if the SSB signal quality does not exceed the second quality threshold, the terminal device 110 may determine in block 880 that the RA procedure has not been completed successfully. That is, if the signal quality of SS-RSRP or similar does not exceed the second quality threshold, the terminal device 110 may perform autonomous retransmission.

[0122] Embodiments of RA procedures without RAR monitoring, or with short RAR monitoring, have been described above. It should be understood that the above signaling flows 500 or processes 600, 800, and 860 can be executed individually or in any appropriate combination. By using these signaling flows or processes, the duration of the RA procedure can be reduced, thereby reducing mobility delays.

[0123] Example of RAR monitoring In some scenarios, in a RA procedure between a serving cell (also called the first cell) and a non-serving cell (also called the second cell), monitoring the RAR allows the terminal device to acquire the TA earlier. Therefore, under certain circumstances, the terminal device may perform RAR monitoring to gain an advantage.

[0124] According to some legacy mechanisms, the PDCCH candidate group monitored by a terminal device is defined by a PDCCH SS set. The SS set can be a common search space (CSS) set or a terminal-specific search space (USS) set. The terminal device monitors PDCCH candidates in one or more of the following search space sets: the Type1-PDCCH CSS set, configured by the ra-SearchSpace in PDCCH-ConfigCommon for DCI formats with CRCs scrambled by RA-RNTI or temporary C-RNTI (TC-RNTI) on the primary cell.

[0125] If a terminal device is provided with one or more search area sets by supporting one or more of the following: searchSpaceZero, searchSpaceSIB1, searchSpaceOtherSystemInformation, pagingSearchSpace, ra-SearchSpace, and C-RNTI, modulation and coding scheme (MCS)-C-RNTI, or CS (configured scheduling)-RNTI, then in a slot where the terminal device monitors PDCCH candidates of DCI format 0_0 or DCI format 1_0 having CRCs scrambled by system information (SI)-RNTI, RA-RNTI, or P(padding)-RNTI, the terminal device monitors PDCCH candidates of DCI format 0_0 and DCI format 1_0 having CRCs scrambled by C-RNTI, MCS-C-RNTI, or CS-RNTI in one or more search area sets.

[0126] According to the legacy mechanism described above, terminal devices used various RNTIs for RAR monitoring under different conditions. It is necessary to consider the detailed operation of how RNTIs are used for RAR monitoring, or which RNTIs are used for RAR monitoring. This disclosure proposes several detailed solutions for RAR monitoring using RNTIs, which will be explained with reference to Figures 9A to 10.

[0127] In the following embodiments relating to Figures 9A to 10, it is assumed that terminal device 110 is currently being serviced by cell 122-1 (referred to as the "first cell" or "serving cell") of network device 120-1 (referred to as the "first network device" or "serving network device"). Terminal device 110 receives a PDCCH order from network device 120-1 indicating the cell to initiate the RA procedure. Cell 122-2 (referred to as the "second cell", "candidate cell", or "target cell") of network device 120-2 (referred to as the "second network device") is the cell for handover.

[0128] Figure 9A shows a process 900 for monitoring RAR with RNTI according to some exemplary embodiments of the present disclosure. For convenience of explanation, the process 900 will be described in terms of the terminal device 110 in Figure 1.

[0129] In block 910, the terminal device 110 determines whether it is configured to monitor the RAR for the RA procedure. If the terminal device 110 is configured to monitor the RAR, in block 920, the terminal device 110 monitors the RAR by monitoring the DCI using at least one of a first C-RNTI configured for a first cell, such as cell 122-1, or a second C-RNTI configured for a second cell, such as cell 122-2. As an example, the terminal device 110 may monitor the RAR by monitoring the DCI using a second C-RNTI configured for cell 122-1 without using a first C-RNTI.

[0130] By using process 900, terminal device 110 can initiate the application of common cell settings, including type 1SS settings and / or C-RNTI values, to candidate cells such as cell 122-2. Terminal device 110 monitors DCI on the search area of ​​a serving cell (e.g., cell 122-1) using the C-RNTI of the serving cell and monitors DCI on the search area of ​​a non-serving cell (candidate cell) (e.g., cell 122-2) using the C-RNTI of the non-serving cell. This improves PDCCH monitoring.

[0131] Figure 9B shows another process 950 for monitoring RAR with RNTI, according to some exemplary embodiments of this disclosure. For convenience of explanation, process 950 will be described in terms of the terminal device 110 in Figure 1.

[0132] Similar to process 900, in block 910, the terminal device 110 determines whether it is configured to monitor the RAR for the RA procedure. If the terminal device 110 is configured to monitor the RAR, in block 960, the terminal device 110 may monitor the RAR by skipping DCI monitoring using a second C-RNTI configured for a second cell, such as cell 122-2.

[0133] In block 970, the terminal device 110 determines whether a search area for monitoring DCI is set for a second cell, such as cell 122-2. If a search area is set for a second cell, in block 980, the terminal device 110 may skip monitoring DCI by skipping at least one DCI opportunity within the search area.

[0134] In other words, terminal device 110 does not need to apply C-RNTI set for candidate cells such as cell 122-2. When the search area is on a non-serving cell (a candidate cell for handover) such as cell 122-2, in a slot where terminal device 110 monitors PDCCH candidates of DCI format 0_0 or DCI format 1_0 having a CRC scrambled by at least SI-RNTI, RA-RNTI, or P-RNTI, terminal device 110 does not monitor PDCCH candidates of DCI format 0_0 and DCI format 1_0 having a CRC scrambled by C-RNTI within one or more sets of search areas.

[0135] The reason is that C-RNTI is a value set for each cell. A candidate cell may have the same C-RNTI set for another terminal device. If a terminal device still monitors this C-RNTI on a candidate cell, scheduling for other terminal devices will be incorrectly performed for that terminal device. Therefore, using process 950 can improve RAR monitoring and resource scheduling.

[0136] In some embodiments, the terminal device 110 may ignore UL grants on candidate cells such as cell 122-2. If RACH is completed on a candidate cell such as cell 122-2, the terminal device 110 may stop applying common cell settings, including the Type 1 search area setting and / or C-RNTI value set for the candidate cell.

[0137] In an embodiment in which terminal device 110 monitors RA by monitoring DCI using at least one of a first C-RNTI set for a first cell such as cell 122-1, or a second C-RNTI set for a second cell such as cell 122-2, terminal device 110 may perform RA preamble retransmission under certain circumstances. Figure 10 shows a signaling flow 1000 for RA preamble retransmission according to some exemplary embodiments of the present disclosure. As shown in Figure 10, the signaling flow 1000 involves terminal device 110 and network device 120-2 in Figure 1. Terminal device 110 is serviced in cell 122-1 (also called the "first cell" or "serving cell") of network device 120-1 (referred to as the "first network device"). Cell 122-2 (also called the "second cell" or "candidate cell" or "target cell") of network device 120-2 is a cell for handover. The signaling flow 1000 may involve more or fewer devices, and the number of devices shown in Figure 10 is for illustrative purposes only and does not imply any limitations.

[0138] In operation, before terminal device 110 switches to cell 122-2, terminal device 110 and network device 120-1 perform RA procedures (1010). Network device 120-2 sends a third PDCCH order in DCI to terminal device 110 using a second C-RNTI set for cell 122-2 (1020). The third PDCCH order indicates cell 122-2. In some exemplary embodiments, the third PDCCH order further indicates a second RA resource. Terminal device 110 may receive the third PDCCH order (1030).

[0139] In some embodiments, the terminal device 110 determines whether the reception of the RAR was not completed successfully and whether the DCI was detected from the network device 120-2 using a second C-RNTI (1040). If the reception of the RAR was not completed successfully and the DCI was detected from the network device 120-2 using a second C-RNTI, the terminal device 110 determines whether the third PDCCH order included in the DCI indicates a second cell, such as cell 122-2 (1050). If the third PDCCH order indicates cell 122-2, the terminal device 110 may stop monitoring the RAR (1070). Furthermore, if the third PDCCH order indicates cell 122-2, the terminal device 110 may perform a retransmission of the RA preamble in the RA procedure. For example, the terminal device 110 sends the RA preamble to the network device 120-2 (1070). If the transmission is successful, network device 120-2 receives the RA preamble (1080).

[0140] Alternatively or additionally, in some embodiments, if the third PDCCH order indicates a second cell, the terminal device 110 may determine whether the third PDCCH order indicates a second RA resource. If the third PDCCH order indicates a second RA resource, the terminal device 110 may stop monitoring the RAR (1060) and perform a retransmission of the RA preamble in the RA procedure.

[0141] If, by executing the signaling flow 1000, the RAR does not complete successfully and a PDCCH order is received addressed to the target C-RNTI of the target cell set by the RRC, and / or if the PDCCH order shows the same random access preamble, PRACH mask index, and uplink carrier as set by the RRC, the terminal device 110 may stop the RAR timer and consider that RACH is not complete. For example, the terminal device 110 may immediately retransmit the RACH preamble.

[0142] In this way, early notification of preamble misdetection by the network and corresponding retransmission instructions to the terminal device 110 become possible, further reducing RACH delays and / or serving cell interruptions for candidate cells. Therefore, the terminal device 110 can perform preamble retransmission earlier to reduce delays when RAR is configured to monitor.

[0143] While some exemplary specifications and embodiments are provided above, please understand that detailed descriptions may be modified.

[0144] Exemplary embodiments of RA procedure initiation, RACH initiation and RAR monitoring, RA procedures without RAR monitoring, and RAR monitoring have been described above with reference to signaling flows 200, 400, 500, 1000 and processes 300, 600, 800, 860, 900, 950. In some embodiments, embodiments described with reference to two or more of the above signaling flows and processes can be combined. By using these signaling flows and / or processes, L1 / L2-based inter-cell mobility or LTM can be improved. In particular, mobility delay can be reduced. Exemplary Method

[0145] Figure 11 shows a flowchart of a communication method 1100 implemented in a terminal device according to some embodiments of this disclosure. For convenience of explanation, the method 1100 will be described in terms of the terminal device 110 in Figure 1.

[0146] In block 1110, terminal device 110 receives a first physical downlink control channel (PDCCH) order from a first network device, such as network device 120-1, to trigger a random access (RA) procedure. The first PDCCH order indicates a first RA resource.

[0147] In block 1120, terminal device 110 determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover (e.g., network device 120-2). Terminal device 110 is being served in the first cell.

[0148] In block 1130, if the first PDCCH order indicates the second cell, the terminal device 110 ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource. The second RA resource is configured for the terminal device 110 by the second network device.

[0149] In some exemplary embodiments, if the first PDCCH order indicates a first cell, the terminal device 110 may initiate an RA procedure toward the first network device using the first RA resource.

[0150] In some exemplary embodiments, the second RA resource includes a non-collision RA (CFRA) resource.

[0151] In some exemplary embodiments, if a first PDCCH order indicates a second cell, the terminal device 110 may determine whether at least one of a plurality of candidate synchronization signal blocks (SSBs) associated with the RA opportunity has a signal quality exceeding a first quality threshold. If at least one SSB has a signal quality exceeding the first quality threshold, the terminal device 110 may initiate the RA procedure using the CFRA resources based on at least one SSB. If none of the plurality of candidate SSBs have a signal quality exceeding the first quality threshold, the terminal device 110 may initiate the RA procedure using the CFRA resources based on at least one of the plurality of candidate SSBs.

[0152] In some exemplary embodiments, in response to a handover command, terminal device 110 may perform a handover procedure from the first cell to the second cell. If the timing advance (TA) information of the second cell is unavailable or invalid, terminal device 110 uses CFRA resources to initiate a further RA procedure toward the second cell and monitors for further RARs for the further RA procedure from the second network device, regardless of whether terminal device 110 is configured to monitor RA Responses (RARs). The further RARs indicate at least the TA information of the second cell.

[0153] In some exemplary embodiments, if the terminal device 110 is configured not to monitor the RAR for the RA procedure, the terminal device 110 may determine that the RA procedure has completed successfully after it has started.

[0154] In some exemplary embodiments, if terminal device 110 is configured not to monitor RAR for an RA procedure, terminal device 110 may determine that the RA procedure has not completed successfully after it has started. Terminal device 110 may transmit an RA preamble to a second network device a predetermined number of times during the RA procedure. Terminal device 110 may determine that the RA procedure has completed successfully after the RA preamble has been transmitted a predetermined number of times.

[0155] In some exemplary embodiments, the terminal device 110 may monitor the RAR for an RA procedure by setting the RA timer to zero. If the RAR timer expires, the terminal device 110 may determine that the RA preamble in the RA procedure was transmitted on the secondary cell (SCell). If the RA preamble was transmitted on the SCell, the terminal device 110 may determine that the RA procedure did not complete successfully.

[0156] In some exemplary embodiments, if the terminal device 110 is configured not to monitor RAR for the RA procedure, the terminal device 110 may determine that the RA procedure is not complete. The terminal device 110 may increment the retransmission counter in the RA preamble of the RA procedure. If the RA procedure is not complete and the retransmission counter is within the retransmission upper threshold, the terminal device 110 may determine whether a second PDCCH order indicating a second cell has been received. If a second PDCCH order indicating a second cell has been received, the terminal device 110 may perform the RA resource selection procedure.

[0157] In some exemplary embodiments, if the terminal device 110 is configured not to monitor RAR for the RA procedure, the terminal device 110 may determine whether the signal quality of the SSB for initiating the RA procedure exceeds a second quality threshold. If the signal quality of the SSB exceeds the second quality threshold, the terminal device 110 may determine that the RA procedure has completed successfully. If the signal quality of the SSB does not exceed the second quality threshold, the terminal device 110 may determine that the RA procedure has not completed successfully.

[0158] In some exemplary embodiments, if the terminal device 110 is configured to monitor RAR for RA procedures, the terminal device 110 may monitor RAR by monitoring downlink control information (DCI) using at least one of a first cell radio network temporary identifier (C-RNTI) set for a first cell or a second C-RNTI set for a second cell.

[0159] In some exemplary embodiments, if the reception of the RAR is not completed successfully and the DCI is detected from the second network device using the second C-RNTI, the terminal device 110 may determine whether the third PDCCH order included in the DCI indicates the second cell. If the third PDCCH order indicates the second cell, the terminal device 110 may stop monitoring the RAR and perform a retransmission of the RA preamble in the RA procedure.

[0160] In some exemplary embodiments, if a third PDCCH order indicates a second cell, the terminal device 110 may determine whether the third PDCCH order indicates a second RA resource. If the third PDCCH order indicates a second RA resource, the terminal device 110 may stop monitoring the RAR and perform a retransmission of the RA preamble in the RA procedure.

[0161] In some exemplary embodiments, if terminal device 110 is configured to monitor RAR for RA procedures, terminal device 110 may monitor RAR by skipping DCI monitoring using a second C-RNTI configured for a second cell.

[0162] In some exemplary embodiments, the terminal device 110 may determine whether a search area for monitoring DCI is set up for a second cell. If a search area is set up for a second cell, the terminal device 110 may skip monitoring DCI by skipping at least one DCI opportunity within the search area.

[0163] Figure 12 shows a flowchart of a communication method 1200 implemented in a second network device according to some embodiments of the present disclosure. For convenience of explanation, the method 1200 will be described in terms of the network device 120-2 in Figure 1.

[0164] In block 1210, network device 120-2 configures a second random access (RA) resource for a terminal device such as terminal device 110. The terminal device is serviced in the first cell of the first network device such as network device 120-1. The second RA resource includes a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before it switches to the second cell.

[0165] In block 1220, after the terminal device switches from the first cell to the second cell, the network device 120-2 uses the second RA resource to perform further RA procedures with the terminal device.

[0166] In block 1230, the network device 120-2 sends further RARs to the terminal device for further RA procedures, regardless of whether the terminal device is configured to monitor RA responses (RARs). The further RARs indicate timing advance (TA) information for at least the second cell.

[0167] In some exemplary embodiments, network device 120-2 may perform an RA procedure with the terminal device before the terminal device switches to the second cell. Network device 120-2 may transmit a third PDCCH order in the DCI to the terminal device using a second cell radio network temporary identifier (C-RNTI) set for the second cell. The third PDCCH order indicates the second cell. Network device 120-2 may receive a retransmission of the RA preamble in the RA procedure from the terminal device.

[0168] In some exemplary embodiments, a third PDCCH order further indicates a second RA resource. Exemplary device

[0169] Figure 13 is a simplified block diagram of a device 1300 suitable for carrying out embodiments of the present disclosure. Device 1300 can be considered a further exemplary implementation of any of the devices shown in Figure 1. Thus, device 1300 may be implemented in or as at least part of a terminal device 110 or a network device 120.

[0170] As shown in the figure, the device 1300 comprises a processor 1310, a memory 1320 coupled to the processor 1310, a suitable transceiver 1340 coupled to the processor 1310, and a communication interface coupled to the transceiver 1340. The memory 1310 stores at least a portion of the program 1330. The transceiver 1340 may be for bidirectional or unidirectional communication depending on the requirements. The transceiver 1340 may include at least one of a transmitter 1342 and a receiver 1344. The transmitter 1342 and receiver 1344 may be functional modules or physical entities. The transceiver 1340 has at least one antenna to facilitate communication, but in practice, the access node referred to herein may have multiple antennas. The communication interface may represent any interface necessary for communication with other network elements, such as the X2 / Xn interface for bidirectional communication between eNBs / gNBs, the S1 / NG interface for communication between Mobility Management Entity (MME) / Mobility Management Function (AMF) / SGW / UPF and eNBs / gNBs, the Un interface for communication between eNBs / gNBs and relay nodes (RNs), or the Uu interface for communication between eNBs / gNBs and terminal devices.

[0171] Program 1330 is assumed to include program instructions that, when executed by the associated processor 1310, enable the device 1300 to operate according to embodiments of the present disclosure, as described herein with reference to Figures 1 to 12. Embodiments herein may be implemented by computer software executable by the processor 1310 of the device 1300, by hardware, or by a combination of software and hardware. The processor 1310 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1310 and memory 1320 may form processing means 13130 ​​suitable for implementing various embodiments of the present disclosure.

[0172] Memory 1320 may be of any type suitable for the local technology network and may be implemented using any suitable data storage technology, such as non-temporary computer-readable storage media, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as an unrestricted example. Although only one memory 1320 is shown for device 1300, device 1300 may have multiple physically different memory modules. Processor 1310 may be of any type suitable for the local technology network and may include, as an unrestricted example, one or more of general-purpose computers, special-purpose computers, microprocessors, digital signal processors (DSPs), and processors based on multi-core processor architectures. Device 1300 may have multiple processors, such as application-specific integrated circuit chips that are temporally slaved to a clock that synchronizes the main processor.

[0173] Embodiments of the present disclosure provide a terminal device comprising a circuit that receives a first physical downlink control channel (PDCCH) order from a first network device which triggers a random access (RA) procedure, wherein the first PDCCH order indicates a first RA resource, and the terminal device determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device is served in the first cell and, in response to the determination that the first PDCCH order indicates a second cell, ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource, wherein the second RA resource is configured to be set for the terminal device by the second network device. Embodiments of the present disclosure may also configure the circuit to implement any method implemented by the terminal device described above.

[0174] Embodiments of the present disclosure provide a second network device comprising a circuit that configures a second random access (RA) resource for a terminal device, the terminal device being served in a first cell of the first network device, the second RA resource comprising a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to a second cell of the second network device, and after the terminal device switches from the first cell to the second cell, the circuit that uses the second RA resource to perform further RA procedures with the terminal device and sends further RARs to the terminal device for further RA procedures, regardless of whether the terminal device is configured to monitor RA Responses (RARs), the further RARs are configured to indicate at least timing advance (TA) information for the second cell. Embodiments of the present disclosure may configure the circuit to implement any method implemented by the second network device as described above.

[0175] Embodiments of the present disclosure provide a communication method comprising a circuit that determines whether a first PDCCH order indicates a first cell of a first network device or a second cell of a second network device for handover, and the terminal device is serviced in the first cell and, in response to the determination that the first PDCCH order indicates the second cell, ignores a first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using a second RA resource, the second RA resource being configured to be set for the terminal device by the second network device. Embodiments of the present disclosure may be configured to implement any method implemented by the communication method described above.

[0176] As used herein, the term “circuit” may refer to a hardware circuit and / or a combination of a hardware circuit and software. For example, a circuit may be a combination of an analog and / or digital hardware circuit and software / firmware. As a further example, a circuit may be any part of a hardware processor having software, and a hardware processor may include a digital signal processor(s), software, and memory(s) that work together to enable a device, such as a terminal or network device, to perform various functions. In yet another example, a circuit may be a hardware circuit and / or processor, such as a microprocessor or a part of a microprocessor, which requires software / firmware for operation, but the software may not be present when not required for operation. As used herein, the term “circuit” may also include simply a hardware circuit or processor(s) or a part of a hardware circuit or processor(s) and the implementation of the software and / or firmware associated with it (or them).

[0177] In summary, embodiments of this disclosure provide the following aspects.

[0178] In one embodiment, a terminal device is proposed comprising a processor, the processor receiving a first physical downlink control channel (PDCCH) order from a first network device to trigger a random access (RA) procedure, wherein the first PDCCH order indicates a first RA resource, and the processor determines whether the first PDCCH order indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device is serviced in the first cell and, in response to the determination that the first PDCCH order indicates a second cell, ignores the first RA resource in the first PDCCH order and initiates an RA procedure toward the second cell using the second RA resource, wherein the second RA resource is configured to be set for the terminal device by the second network device.

[0179] In some embodiments, the processor is further configured to initiate an RA procedure toward a first network device using a first RA resource in response to a determination that a first PDCCH order indicates a first cell.

[0180] In some embodiments, the second RA resource includes a non-collision RA (CFRA) resource.

[0181] In some embodiments, the processor is further configured to determine, in response to a determination that a first PDCCH order indicates a second cell, whether at least one of a plurality of candidate synchronization signal blocks (SSBs) associated with an RA opportunity has a signal quality exceeding a first quality threshold; in response to a determination that at least one SSB has a signal quality exceeding the first quality threshold, to initiate an RA procedure using CFRA resources based on at least one SSB; and in response to a determination that none of the plurality of candidate SSBs have a signal quality exceeding the first quality threshold, to initiate an RA procedure using CFRA resources based on at least one of the plurality of candidate SSBs.

[0182] In some embodiments, the processor further instructs a terminal device to perform a handover procedure from a first cell to a second cell in response to a handover command; to initiate a further RA procedure toward the second cell using CFRA resources, depending on the determination that the timing advance (TA) information of the second cell is unavailable or invalid; and to monitor further RARs for further RA procedures from the second network device, regardless of whether the terminal device is configured to monitor RA Responses (RARs), wherein the further RARs are configured to indicate at least the TA information of the second cell.

[0183] In some embodiments, the processor is further configured to determine that an RA procedure has been successfully completed after it has started, in response to a decision that the terminal device is configured not to monitor RAR for the RA procedure.

[0184] In some embodiments, the processor is further configured to determine, in response to a decision that the terminal device is configured not to monitor RAR for an RA procedure, that an RA procedure has not been successfully completed after it has started, that during the RA procedure it sends an RA preamble to a second network device a predetermined number of times, and that after the RA preamble has been sent a predetermined number of times it determines that the RA procedure has been successfully completed.

[0185] In some embodiments, the processor is further configured to monitor the RAR for an RA procedure by setting the RAR timer to zero, to determine that the RA preamble in the RA procedure has been sent on a secondary cell (SCell) upon determination that the RAR timer has expired, and to determine that the RA procedure has not been successfully completed upon determination that the RA preamble has been sent on a SCell.

[0186] In some embodiments, the processor is further configured to configure the terminal device to determine, in response to a decision that the terminal device is configured not to monitor RAR for the RA procedure, that the RA procedure is incomplete, increment the retransmission counter in the RA preamble in the RA procedure, determine, in response to a decision that the RA procedure is incomplete and the retransmission counter is within the retransmission upper threshold, determine whether a second PDCCH order indicating a second cell has been received, and execute the RA resource selection procedure in response to a decision that a second PDCCH order indicating a second cell has been received.

[0187] In some embodiments, the processor is further configured to configure the terminal device to determine, in response to a decision that the terminal device is configured not to monitor RAR for the RA procedure, whether the signal quality of the SSB for initiating the RA procedure exceeds a second quality threshold; in response to the decision that the signal quality of the SSB exceeds the second quality threshold, whether the RA procedure has been successfully completed; and in response to the decision that the signal quality of the SSB does not exceed the second quality threshold, whether the RA procedure has not been successfully completed.

[0188] In some embodiments, the processor is further configured to monitor RAR in a terminal device by monitoring downlink control information (DCI) using at least one of a first cell radio network temporary identifier (C-RNTI) configured for a first cell or a second C-RNTI configured for a second cell, in response to a decision that the terminal device is configured to monitor RAR for RA procedures.

[0189] In some embodiments, the processor is further configured to determine whether a third PDCCH order included in the DCI indicates a second cell, in response to a determination that RAR reception has not been successfully completed and that a DCI has been detected from a second network device using a second C-RNTI, and to stop monitoring the RAR and to retransmit the RA preamble in the RA procedure, in response to a determination that the third PDCCH order indicates a second cell.

[0190] In some embodiments, the processor is further configured to determine, upon the determination that the third PDCCH order indicates a second cell, whether the third PDCCH order indicates a second RA resource, and upon the determination that the third PDCCH order indicates a second RA resource, to stop monitoring the RAR and to retransmit the RA preamble in the RA procedure.

[0191] In some embodiments, the processor is further configured to monitor the RAR by skipping DCI monitoring using a second C-RNTI configured for a second cell, depending on the decision that the terminal device is configured to monitor the RAR for the RA procedure.

[0192] In some embodiments, the processor is further configured to determine whether a search area for monitoring DCI is set for a second cell, and, in response to the determination that a search area is set for the second cell, to skip monitoring DCI by skipping at least one DCI opportunity within the search area.

[0193] In one embodiment, a second network device is proposed, comprising a processor, the processor configuring the second network device for a second random access (RA) resource for a terminal device, the terminal device being served in a first cell of the first network device, the second RA resource including a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to the second cell, and after the terminal device switches from the first cell to the second cell, the processor using the second RA resource to perform further RA procedures with the terminal device and sending further RARs to the terminal device for further RA procedures, regardless of whether the terminal device is configured to monitor RA responses (RARs), the further RARs are configured to indicate at least TA information for the second cell.

[0194] In some embodiments, the processor further instructs the second network device to perform an RA procedure with the terminal device before the terminal device switches to the second cell, and to transmit a third PDCCH order in the DCI to the terminal device using a second cell radio network temporary identifier (C-RNTI) set for the second cell, the third PDCCH order indicating the second cell and set to receive a retransmission of the RA preamble in the RA procedure from the terminal device.

[0195] In some embodiments, a third PDCCH order further indicates a second RA resource.

[0196] In one embodiment, the terminal device comprises at least one processor and at least one memory coupled to the at least one processor, which stores instructions, and when the instructions are executed by the at least one processor, the device causes the device to perform the method implemented by the terminal device described above.

[0197] In one embodiment, the second network device comprises at least one processor and at least one memory coupled to the at least one processor, which stores instructions, and when the instructions are executed by the at least one processor, causes the device to perform the method implemented by the second network device described above.

[0198] In one embodiment, a computer-readable medium, when executed on at least one processor, stores instructions that cause at least one processor to perform the method implemented by the terminal device described above.

[0199] In one embodiment, a computer-readable medium, when executed on at least one processor, stores instructions that cause at least one processor to perform the method implemented by the second network device described above.

[0200] In one embodiment, a computer program, when executed on at least one processor, includes instructions that cause at least one processor to perform the method implemented by the terminal device described above.

[0201] In one embodiment, a computer program, when executed on at least one processor, includes instructions that cause at least one processor to perform the method implemented by the second network device described above.

[0202] Generally, various embodiments of the present disclosure may be implemented in hardware or special-purpose circuits, software, logic, or any combination thereof. Some embodiments may be implemented in hardware, while others may be implemented in firmware or software that can be executed by a controller, microprocessor, or other computing device. Various embodiments of the present disclosure are illustrated and described using block diagrams, flowcharts, or any other pictorial representation, but it should be understood that the blocks, devices, systems, techniques, or methods described herein may be implemented, in non-limiting examples, in hardware, software, firmware, special-purpose circuits or logic, general-purpose hardware or controllers, or other computing devices, or any combination thereof.

[0203] This disclosure also provides at least one computer program product stored tangibly on a non-temporary computer-readable storage medium. The computer program product includes computer-executable instructions (such as computer-executable instructions contained in a program module) that are executed on a device on a target real or virtual processor to perform the processes or methods described above with reference to Figures 1 to 12. Generally, a program module includes routines, programs, libraries, objects, classes, components, data structures, etc., that perform a specific task or implement a specific abstract data type. The functions of the program modules may be combined or divided amongst the program modules as desired in various embodiments. The machine-executable instructions to the program modules may be executed locally or within a distributed device. In a distributed device, the program modules may be located on both local and remote storage media.

[0204] Program code for carrying out the methods of this disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when executed by the processor or controller, the program codes perform functions / operations specified in flowcharts and / or block diagrams. The program codes may run entirely on a machine, partially on a machine, as a standalone software package, partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0205] The above program code may be embodied in a machine-readable medium, which may be any tangible medium that contains or can store a program for use by or in conjunction with an instruction execution system, device, or device. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium includes, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or devices, or any suitable combination thereof. More specific examples of machine-readable storage media include electrical connections having one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, CD-ROMs, optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0206] Furthermore, although the operations are described in a specific order, it should not be understood that, in order to achieve the desired result, such operations must be performed in a specific order shown, or sequentially, or that all illustrated operations must be performed. In certain circumstances, multitasking and parallel processing may be advantageous. Similarly, although some specific implementation details are included in the above description, these should not be interpreted as limiting the scope of this disclosure, but rather as descriptions of features that may be specific to a particular embodiment. Certain features described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately or in any suitable subcombination in multiple embodiments.

[0207] While this disclosure has been described in language specific to structural features and / or methodological behavior, it should be understood that the disclosure as defined in the appended claims is not necessarily limited to the specific features or behaviors described above. Rather, the specific features and behaviors described above are disclosed as exemplary forms of implementing the claims.

Claims

1. A terminal device equipped with a processor, The processor is connected to the terminal device, Receiving a first physical downlink control channel (PDCCH) order from a first network device that triggers a random access (RA) procedure, wherein the first PDCCH order indicates a first RA resource. The first PDCCH order determines whether it indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device receives service in the first cell. In response to the determination that the first PDCCH order indicates the second cell, the first RA resource in the first PDCCH order is ignored, and the RA procedure is initiated toward the second cell using the second RA resource, wherein the second RA resource is configured for the terminal device by the second network device. It is set to be Terminal device.

2. The processor further provides the terminal device with: In response to the determination that the first PDCCH order indicates the first cell, the system is configured to initiate the RA procedure toward the first network device using the first RA resource. The terminal device according to claim 1.

3. The terminal device according to claim 1, wherein the second RA resource includes a non-collision type RA (CFRA) resource.

4. The processor further provides the terminal device with: In response to the determination that the first PDCCH order indicates the second cell, it is determined whether at least one of the multiple candidate synchronization signal blocks (SSBs) associated with the RA opportunity has a signal quality exceeding a first quality threshold. In response to the determination that the at least one SSB has a signal quality exceeding the first quality threshold, the RA procedure is initiated using the CFRA resources based on the at least one SSB. In response to the determination that none of the plurality of candidate SSBs have a signal quality exceeding the first quality threshold, the RA procedure is configured to be initiated using the CFRA resource based on at least one of the plurality of candidate SSBs. The terminal device according to claim 3.

5. The processor further provides the terminal device with: In response to a handover command, the handover procedure from the first cell to the second cell is performed. In response to a determination that the timing advance (TA) information for the second cell is unavailable or invalid, a further RA procedure is initiated toward the second cell using the CFRA resources. Regardless of whether the terminal device is configured to monitor RA responses (RARs), monitoring further RARs for the further RA procedure from the second network device, wherein the further RARs are configured to indicate at least the TA information of the second cell. The terminal device according to claim 3.

6. The processor further provides the terminal device with: In response to the decision that the terminal device is configured not to monitor the RAR for the RA procedure, it is configured to determine that the RA procedure has been successfully completed after it has been initiated. The terminal device according to claim 1.

7. The processor further provides the terminal device with: In response to the decision that the terminal device is configured not to monitor the RAR for the RA procedure, it is determined that the RA procedure has not been completed successfully after it has been started. During the RA procedure, the RA preamble is transmitted to the second network device a predetermined number of times. The system is configured to determine that the RA procedure has been successfully completed after the RA preamble has been transmitted a predetermined number of times. The terminal device according to claim 1.

8. The processor further provides the terminal device with: By setting the RAR timer to zero, the RAR for the RA procedure is monitored. In response to the determination that the RAR timer has expired, it is determined that the RA preamble in the RA procedure has been transmitted on the secondary cell (SCell). In response to the determination that the RA preamble has been sent on SCell, the system is configured to determine that the RA procedure has not been successfully completed. The terminal device according to claim 1.

9. The processor further provides the terminal device with: In response to the decision that the terminal device is configured not to monitor the RAR for the RA procedure, it is determined that the RA procedure is not complete. The retransmission counter in the RA preamble in the aforementioned RA procedure is incremented. In response to the determination that the RA procedure is not completed and the retransmission counter is within the retransmission upper threshold, it is determined whether a second PDCCH order indicating the second cell has been received. In response to the determination that the second PDCCH order indicating the second cell has been received, the system is configured to perform the RA resource selection procedure. The terminal device according to claim 1.

10. The processor further provides the terminal device with: In response to the decision that the terminal device is configured not to monitor the RAR for the RA procedure, it is determined whether the SSB signal quality for initiating the RA procedure exceeds a second quality threshold. In response to the determination that the signal quality of the SSB exceeds the second quality threshold, it is determined that the RA procedure has been successfully completed. The system is configured to determine that the RA procedure has not been completed successfully, based on the determination that the signal quality of the SSB does not exceed the second quality threshold. The terminal device according to claim 1.

11. The processor further provides the terminal device with: In response to a decision that the terminal device is configured to monitor the RAR for the RA procedure, it is configured to monitor the RAR by monitoring downlink control information (DCI) using at least one of a first cell radio network temporary identifier (C-RNTI) set for the first cell, or a second C-RNTI set for the second cell. The terminal device according to claim 1.

12. The processor further provides the terminal device with: If the reception of the RAR has not been completed successfully, and it has been determined that the DCI has been detected from the second network device using the second C-RNTI, then it is determined whether the third PDCCH order included in the DCI indicates the second cell. In accordance with the determination that the third PDCCH order indicates the second cell, Stop monitoring the aforementioned RAR, and The RA procedure in the above RA procedure is to retransmit the RA preamble. It is set to be The terminal device according to claim 11.

13. The processor further provides the terminal device with: In response to the determination that the third PDCCH order indicates the second cell, it is determined whether the third PDCCH order further indicates the second RA resource. In response to the determination that the third PDCCH order indicates the second RA resource, Stop monitoring the aforementioned RAR, and The RA procedure in the above RA procedure is to retransmit the RA preamble. It is set to be The terminal device according to claim 12.

14. The processor further provides the terminal device with: In response to the decision that the terminal device is configured to monitor the RAR for the RA procedure, the monitoring of the DCI using the second C-RNTI configured for the second cell is skipped, thereby enabling the monitoring of the RAR. The terminal device according to claim 1.

15. A second network device comprising a processor, The processor is connected to the second network device, Setting up a second random access (RA) resource for a terminal device, wherein the terminal device is serviced in a first cell of a first network device, and the second RA resource includes a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to a second cell of the second network device. After the terminal device switches from the first cell to the second cell, further RA procedures are performed with the terminal device using the second RA resource. Regardless of whether the terminal device is configured to monitor RA responses (RARs), the further RAR for the further RA procedure is transmitted to the terminal device, wherein the further RAR indicates at least the timing advance (TA) information of the second cell. It is set to be The second network device.

16. The processor further provides the second network device with: Before the terminal device switches to the second cell, the RA procedure is executed with the terminal device. The method involves transmitting a third PDCCH order in the DCI to the terminal device using a second cell radio network temporary identifier (C-RNTI) set for the second cell, wherein the third PDCCH order indicates the second cell. The terminal device is configured to receive a retransmission of the RA preamble in the RA procedure. The second network device according to claim 15.

17. The second network device according to claim 16, wherein the third PDCCH order further indicates the second RA resource.

18. The terminal device receives a first physical downlink control channel (PDCCH) order from a first network device that triggers a random access (RA) procedure, wherein the first PDCCH order further indicates a first RA resource. The first PDCCH order determines whether it indicates a first cell of the first network device or a second cell of a second network device for handover, wherein the terminal device receives service in the first cell. In response to the determination that the first PDCCH order indicates the second cell, the first RA resource in the first PDCCH order is ignored, and the RA procedure is initiated toward the second cell using the second RA resource, wherein the second RA resource is configured for the terminal device by the second network device. A communication method that includes this.

19. The second network device configures a second random access (RA) resource for a terminal device, wherein the terminal device is serviced in a first cell of the first network device, and the second RA resource includes a non-collision RA (CFRA) resource for the terminal device to initiate an RA procedure before the terminal device switches to the second cell. After the terminal device switches from the first cell to the second cell, further RA procedures are performed with the terminal device using the second RA resource. Regardless of whether the terminal device is configured to monitor RA responses (RARs), the further RAR for the further RA procedure is transmitted to the terminal device, wherein the further RAR indicates at least the TA information of the second cell. A communication method that includes this.

20. When executed on at least one processor, the at least one processor stores an instruction causing it to execute the method according to claim 18 or the method according to claim 19. Computer-readable media.

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