Hierarchical failure recovery method and device based on NTN (Network Temporary Network) and RACH (Random Access Channel)-free switching

Abstract

The invention discloses a hierarchical failure recovery method and device based on NTN (Network Temporary Network) RACH (Random Access Channel)-free switching, and belongs to the technical field of wireless communication, and the method comprises the following steps: obtaining timing data of a TAT timer, a T430 timer and a T304 timer; judging a failure level without RACH switching according to the timing data, wherein the failure level comprises a mild failure, a moderate failure and a severe failure; and performing RACH-free switching failure recovery processing according to the failure level pair. Aiming at a failure scene without RACH switching in the NTN, a three-level layered recovery mechanism is designed based on the severity of failure reasons, the interruption time is reduced through a differentiated processing flow, the signaling overhead is reduced, and the recovery robustness is improved.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a hierarchical failure recovery method and apparatus based on NTN-based RACH-free handover. Background Technology

[0002] 3GPP Rel-17 positions NTN as a key technology for "ubiquitous communication services," extending terrestrial 5G coverage through satellite communication and solving communication blind spots in remote areas such as deserts, oceans, and high altitudes. NTN does not replace terrestrial networks, but rather achieves full coverage through "space-ground convergence." For example, terrestrial base stations cover densely populated areas, while satellites cover sparsely populated areas, with both working together through a unified 5G standard.

[0003] In NTN, handover refers to the process of a UE switching from its currently connected satellite beam or satellite to another, with the aim of maintaining uninterrupted communication when satellite coverage changes. In NR NTN (non-terrestrial network), RACH-free handover reduces signaling overhead and user data interruption time by skipping the random access procedure, but its failure handling mechanism still has efficiency bottlenecks. NR NTN consists of satellites, terrestrial gateways (including gNBs), and UEs. The service links between satellites and UEs, and the feeder links between gateways and satellites, have large propagation delays. The high-speed movement of low Earth orbit (LEO) satellites also leads to frequent UE handovers, further increasing the probability of failure.

[0004] Currently, after a RACH-less handover failure, a uniform "random access retry" or "RRC reconstruction" procedure is used, regardless of the cause of the failure (such as temporary synchronization deviation, expired ephemeris, or cell unavailability). This uniform recovery procedure leads to excessively long processing times for minor faults (for example, even when only uplink time alignment fails, random access still needs to be performed, adding tens of milliseconds of interruption). When satellite ephemeris or common timing advance (TA) expires, complete system information needs to be repeatedly obtained, resulting in signaling redundancy, unutilized historical cached parameter fragments, and a significant increase in signaling transmission volume. When the target cell is unavailable, there is a lack of a mechanism for rapid handover to a backup satellite, which may lead to long-term disconnections. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hierarchical failure recovery method and apparatus based on NTN-based RACH-free handover, which solves the technical problems of low recovery efficiency, high signaling overhead and insufficient robustness of the existing RACH-free handover failure handling mechanism.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a hierarchical failure recovery method based on NTN-free RACH handover, characterized in that it includes:

[0008] Acquire timing data from TAT timer, T430 timer, and T304 timer;

[0009] The failure level of no RACH handover is determined based on the timing data. The failure level includes mild failure, moderate failure, and severe failure.

[0010] Perform RACH-free handover failure recovery processing based on the failure level.

[0011] Secondly, the present invention provides a hierarchical failure recovery device based on NTN-free RACH handover, comprising:

[0012] The data acquisition module is configured to acquire timing data from the TAT timer, T430 timer, and T304 timer;

[0013] The failure stratification module is configured to determine the failure level of no RACH switching based on the timing data. The failure levels include mild failure, moderate failure, and severe failure.

[0014] The hierarchical recovery module is configured to perform RACH-free handover failure recovery processing based on the failure level.

[0015] Thirdly, the present invention provides an electronic device, including a processor and a storage medium;

[0016] The storage medium is used to store instructions;

[0017] The processor is configured to operate according to the instructions to perform the steps according to the method described above.

[0018] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method.

[0019] Fifthly, the present invention provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the above-described method.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0021] This invention provides a hierarchical failure recovery method and apparatus based on NTN handover without RACH. The method includes the following steps: determining the failure level through timer state combinations (expiration logic of TAT / T430 / T304); for minor failures, the UE calculates the TA adjustment value and sends a correction request through pre-allocated resources; for moderate failures, the UE obtains incremental satellite parameters from the source cell and updates the TA value; for severe failures, the UE prioritizes accessing the same PCI alternative beam or handover to a TN cell. In summary, this invention addresses the failure scenario of NTN handover without RACH by designing a three-level hierarchical recovery mechanism based on the severity of the failure cause. This mechanism reduces downtime, lowers signaling overhead, and improves recovery robustness through differentiated processing flows. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the hierarchical failure recovery method based on NTN-free RACH handover provided in an embodiment of the present invention.

[0023] Figure 2 This is a timing diagram of the RACH-free handover failure recovery process provided in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0025] Example 1:

[0026] like Figure 1 As shown, this invention provides a hierarchical failure recovery method based on NTN-based RACH-free handover, comprising:

[0027] Step S1: Obtain timing data from TAT timer, T430 timer, and T304 timer.

[0028] The TAT timer is an uplink time alignment timer used to control the uplink synchronization status between the user equipment (UE) and the network.

[0029] When the TAT timer expires, it indicates that the uplink transmission time of the user equipment (UE) deviates from the network's expected time by more than a threshold, and time alignment correction (such as a minor failure recovery process) needs to be triggered.

[0030] The T430 timer is a validity timer for satellite ephemeris tables and common timing advances (TA).

[0031] When the T430 timer expires, it indicates that the satellite orbit parameters (ephemeris) or common timing advance (TA) cached by the user equipment (UE) have expired, and parameter updates need to be triggered (such as in the moderate failure recovery process).

[0032] The T304 timer is a handover process timer used to monitor whether a no-RACH handover has timed out.

[0033] When the T304 timer expires, it indicates that the handover process has failed (e.g., the target cell is unavailable), and a higher-level recovery strategy (e.g., a severe failure recovery process) needs to be triggered.

[0034] Step S2: Determine the failure level of no RACH handover based on timing data.

[0035] Specifically, in this embodiment, the failure levels include mild failure, moderate failure, and severe failure.

[0036] If the TAT timer expires, but the T430 and T304 timers have not, the failure level is classified as a minor failure. The essence of this failure is a temporary uplink synchronization deviation (such as timing advance calculation errors caused by UE movement), while core parameters such as satellite ephemeris and common TA remain valid. This applies to short-term mobile scenarios within the LEO satellite beam.

[0037] If the TAT timer and T430 timer expire, but the T304 timer has not expired, the failure level is moderate. The essence of this failure is that the satellite ephemeris or public TA parameters have expired (e.g., due to satellite orbit fine-tuning causing parameter invalidation), but the target cell remains within coverage. This applies to scenarios where satellite orbit parameters are periodically updated.

[0038] If the TAT timer, T430 timer, or T304 timer expires, the failure level is classified as a severe failure. The essence of this failure is that the target cell is unavailable (e.g., satellite beam shifting out of coverage, gateway failure), or the handover process times out. This applies to scenarios where coverage handover failure is caused by high-speed satellite movement.

[0039] Step S3: Perform RACH-free handover failure recovery processing according to the failure level.

[0040] like Figure 2 As shown, specifically in this embodiment, (1) when the failure level is a minor failure, the satellite ephemeris table and common TA parameters cached by the UE are still valid (T430 has not expired), only the uplink time alignment status is invalidated, and the RACH handover failure recovery process includes:

[0041] 1. User Equipment (UE) → Target Cell: Uplink transmission of "TA Correction Request".

[0042] The user equipment calculates the TA adjustment value based on the cached satellite ephemeris (including satellite position and velocity) and its own geographic location (such as GNSS positioning information). It uses pre-allocated uplink resources (such as pre-configured PUSCH resources) to send a timing advance correction request containing the TA adjustment value of the user equipment to the target cell, without initiating random access.

[0043] 2. Target cell → User Equipment (UE): PDCCH sends "Dynamic Uplink Authorization".

[0044] The target cell sends a dynamic uplink grant to the target device through the physical downlink control channel (PDCCH, which uses the user equipment UE's C-RNTI scrambling to ensure that the command is only received by the corresponding user equipment UE). The dynamic uplink grant includes the uplink transmission timing adjusted based on the user equipment TA adjustment value and the new TAT duration.

[0045] 3. UE → Target Cell: Uplink data transmission.

[0046] The user equipment performs uplink data transmission based on the dynamic uplink authorization, sends the first piece of recovered data (such as survey data or status report), and verifies whether the synchronization is effective.

[0047] 4. UE local operation: Restart the TAT timer.

[0048] After confirming successful data transmission, the UE resets the Synchronization Maintenance Timer (TAT) to its initial value (e.g., 100 milliseconds) to maintain subsequent uplink synchronization. Normal communication is then restored, and the entire process does not require rebuilding the Radio Resource Control (RRC) connection.

[0049] (2) When the failure level is moderate, the satellite ephemeris table or public TA parameters have expired (T430 timer expires), but the target cell is still within the coverage area (T304 timer has not expired), and the source cell and the target cell belong to the same ground gateway (parameter caching is supported). The RACH handover failure recovery process includes:

[0050] 1. UE → Source Cell: Signaling sends "Satellite Parameter Incremental Update Request".

[0051] The user equipment sends an incremental satellite parameter update request to the source cell, carrying the physical cell identifier (PCI) of the target cell and the cached satellite ephemeris version number, specifying the content to be updated (such as ephemeris, public TA).

[0052] 2. Source cell → UE: Signaling push "incremental information".

[0053] The source cell retrieves updated segments of the target satellite's ephemeris from its local cache based on the satellite ephemeris version number (such as incremental data for orbital inclination corrections and common TA adjustments). And it is sent to the user equipment via RRC signaling (avoiding the transmission of the complete ephemeris).

[0054] 3. UE local operation: Update TA parameters and complete downlink synchronization.

[0055] User equipment updates the public TA adjustment value by combining historical cached basic parameters with incremental data. User Equipment TA Adjustment Value , , and These are the pre-update data and incremental data of the public TA adjustment value, respectively, and the downlink synchronization of the target cell is completed based on the synchronization signal block of the target satellite and the physical cell identifier of the target cell (calibrating the deviation between the reception time and the satellite transmission time).

[0056] 4. Target cell → UE: PDCCH sends "Dynamic uplink authorization".

[0057] User equipment (UE) listens to the physical downlink control channel (PDCCH) of the target cell (using UE's C-RNTI scrambling) to obtain dynamic uplink authorization.

[0058] 5. UE → Target Cell: Uplink data transmission.

[0059] Send the first uplink data based on the dynamic uplink authorization to verify whether the communication link has been restored.

[0060] 6. UE local operation: Restart the T430 timer.

[0061] After confirming successful transmission, restart the T430 timer (to match the satellite orbit update cycle).

[0062] (3) When the failure level is severe, the target cell is unavailable (e.g., the satellite beam moves out of coverage), and it needs to be switched to the beam of an adjacent satellite in the same constellation (pre-configured as a backup cell). The recovery process for RACH-less handover failure includes:

[0063] 1. UE local operation: Search for alternative beams.

[0064] User equipment, based on a pre-configured list of co-orbiting satellites (including PCI and frequency information of adjacent satellites), prioritizes searching for alternative beams with the same Physical Cell Identifier (PCI) as the target cell (because the frequency and parameters are consistent, the original configuration can be directly reused, reducing synchronization time).

[0065] 2. UE → Alternate Cell: No RACH access request.

[0066] If an available alternative beam exists, the user equipment calculates the TA value using the cached neighbor satellite ephemeris table and sends a RACH-free access request containing the TA value to the alternative cell through pre-allocated uplink resources (reusing the RACH-free handover mechanism), without the need for random access.

[0067] 3. Alternate Cell → UE: Access Response and Uplink Authorization.

[0068] The alternative cell verifies the UE's identity (based on C-RNTI), sends an access response via PDCCH, allocates uplink resources, and confirms successful access.

[0069] 4. UE → Alternate Cell: Resume uplink transmission.

[0070] The UE uses the resources of the alternative cell to send data and complete the communication recovery.

[0071] 5. Last resort branch: Triggers RRC reconstruction when there are no alternative beams.

[0072] If no alternative beam is available, the user equipment triggers the RRC reconstruction process to release the connection with the original cell; based on the pre-configured TN network coverage area information (such as center coordinates 30°N, 120°E, radius 50 km), it searches for and accesses the nearest TN cell, and completes the connection reconstruction through random access.

[0073] Implementation and verification:

[0074] 1. Implementation scenario definition.

[0075] Network environment: Low Earth Orbit (LEO) satellite constellation (orbital altitude 600km), satellite 0 and satellite 1 are adjacent satellites in the same orbit, both providing services through the same ground gateway (gNB), and adopting PCI unchanged cell configuration (same PCI, frequency and cell parameters).

[0076] User Equipment: The UE is within the beam coverage area of ​​satellite 0 and is performing a handover without RACH (Scenario 1: Handover between different beams within the same gateway and satellite).

[0077] Key parameters: TAT=100ms (UL time alignment maintenance period), T430=30s (ephemeris validity period), T304=500ms (handover process timeout threshold).

[0078] 2. Implementation steps.

[0079] 2.1 Initial No-RACH Handover Procedure

[0080] The UE initiates a RACH-free handover to beam 2 in beam 1 of satellite 0, as follows:

[0081] The UE sends a measurement report to the source beam (beam 1), which includes its own approximate location information;

[0082] The source beam indicates the epoch time, ephemeris, and common TA parameters of the target beam (beam 2) via a switching command;

[0083] The UE performs a handover based on the pre-compensated TA, skipping random access;

[0084] The formula for calculating pre-compensation TA is:

[0085] ,in .

[0086] The basic timing advance value (i.e., basic TA adjustment value) is allocated to the UE by the network. In RACH-free handover, ( It is usually set to 0 to simplify the calculation process.

[0087] This is the common timing advance offset (i.e., common TA adjustment value), which is related to the characteristics of the satellite feeder link. It compensates for the propagation delay between the satellite and the ground gateway. This value is shared by all UEs and is broadcast through system information (such as SIB19).

[0088] This is the common switching current (TA) adjustment value for the feeder link, used to correct for time delay differences caused by changes in satellite position. When the satellite orbit is finely adjusted... It will be updated with the ephemeris table to ensure that the TA calculation for all UEs is accurate.

[0089] The TA adjustment value for the user equipment is calculated based on the relative position of the UE and the satellite. Service link propagation delay between the UE and the satellite is compensated, and is calculated independently for each UE (e.g., in the case of a minor failure, the UE recalculates this value based on its own position).

[0090] The UE synchronizes with the target beam, sends the first data through the pre-allocated UL authorization, and the handover is successful.

[0091] 2.2 Layered failure recovery execution process:

[0092] 2.2.1 Mild failure recovery (TAT expired and triggered).

[0093] Triggering conditions: The UE's UL synchronization is deviated due to a slight positional movement, the TAT expires (T430 and T304 have not expired), and the ephemeris and public TA are still valid.

[0094] Recovery steps:

[0095] The UE recalculates based on the cached satellite ephemeris and its own GNSS position. (User Equipment TA Adjustment Value);

[0096] The UE uses pre-allocated UL resources to send a "TA correction request", carrying the new ;

[0097] The target beam feeds back dynamic UL authorization via PDCCH (C-RNTI scrambling), adjusts the transmission timing, and the UE restarts TAT;

[0098] Resume UL transmission with an interruption time of <20ms (without PRACH process).

[0099] 2.2.2 Moderate failure recovery (T430 expired and triggered).

[0100] Triggering condition: Satellite 0 ephemeris expires (T430 expires), but the target beam is still within the coverage area (T304 has not expired).

[0101] Recovery steps:

[0102] The UE sends an "ephemeris increment request" to the source gateway, carrying the current PCI and ephemeris version;

[0103] The gateway pushes incremental data of ephemeris update fragments (such as orbital inclination correction values) and common TA adjustment values ​​for satellite 0. This is used for parameter correction during moderate failure recovery. When T430 expires, the network side only sends ( (not complete) This reduces signaling overhead.

[0104] UE update and DL synchronization is achieved based on the target beam SSB;

[0105] Sending the first data via dynamic UL authorization and restarting the T430 reduces the signaling volume compared to a full SIB19 transmission.

[0106] 2.2.3 Severe failure recovery (triggered by T304 expiration)

[0107] Triggering conditions: Satellite 0 beam moves out of coverage, handover timeout (T304 expires), target beam is unavailable.

[0108] Recovery steps:

[0109] The UE initiates alternative beam search and locks onto satellite 1 (PCI unchanged cell) based on the pre-configured list of co-orbital satellites.

[0110] The UE uses the cached ephemeris table of satellite 1 to calculate the TA and sends an access request through RACH-free access (multiplexing scenario 4: handover between different satellites of the same gateway).

[0111] Satellite 1 authorizes UL resources via PDCCH, UE resumes transmission, and T304 restarts;

[0112] If satellite 1 is unavailable, the UE will switch to a ground cell based on the TN coverage area information (center coordinates + radius) in SIB25 to avoid disconnection.

[0113] 3. Key Configuration Description:

[0114] For cells with unchanged PCI, satellite 0 and satellite 1 share PCI=100;

[0115] SIB19 content, ephemeris, public TA, beam coverage;

[0116] T430 duration, 30s (matching the LEO satellite orbit update cycle);

[0117] SIB25 includes 3 TN coverage areas (center coordinates + radius).

[0118] The embodiments of the present invention have the following characteristics:

[0119] 1. Reduce service interruption time: Minor failures eliminate the random access process, reducing interruption by 25-50ms (LEO satellite scenario) compared to the existing mechanism; severe failures prioritize access to pre-configured alternative beams, shortening recovery time to 1 / 3 of the existing mechanism.

[0120] 2. Reduce signaling overhead: Moderate failures reduce signaling by more than 60% compared to transmitting complete system information through incremental parameter updates, making it particularly suitable for scenarios with limited satellite link bandwidth.

[0121] 3. Adapting to satellite movement characteristics: The recovery strategy is designed based on the periodicity of satellite orbits and the invariance of PCI to match the frequent handover requirements caused by the high-speed movement of LEO satellites.

[0122] 4. Improve robustness: In the event of severe failure, combine TN coverage area information to quickly switch to the terrestrial network when satellite coverage is lost, avoiding long-term disconnection.

[0123] Example 2:

[0124] This invention provides a hierarchical failure recovery device based on NTN-free RACH handover, comprising:

[0125] The data acquisition module is configured to acquire timing data from the TAT timer, T430 timer, and T304 timer;

[0126] The failure stratification module is configured to determine the failure level of no RACH switching based on timing data. The failure levels include minor failure, moderate failure, and severe failure.

[0127] The tiered recovery module is configured to perform RACH-free handover failure recovery based on the failure level.

[0128] Example 3:

[0129] Based on the layered failure recovery method provided in Embodiment 1, this embodiment of the invention provides an electronic device, including a processor and a storage medium;

[0130] Storage media are used to store instructions;

[0131] The processor is used to perform operations according to instructions to execute the steps according to the method described above.

[0132] Example 4:

[0133] Based on the hierarchical failure recovery method provided in Embodiment 1, this embodiment of the invention provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the above method.

[0134] Example 5:

[0135] Based on the hierarchical failure recovery method provided in Embodiment 1, this embodiment of the invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of the above-described method.

[0136] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0137] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0138] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0139] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0140] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A hierarchical failure recovery method based on NTN-based RACH-free handover, characterized in that, include: Acquire timing data from TAT timer, T430 timer, and T304 timer; The failure level of no RACH handover is determined based on the timing data. The failure level includes mild failure, moderate failure, and severe failure. Perform RACH-free handover failure recovery processing based on the failure level.

2. The hierarchical failure recovery method based on NTN-free RACH handover according to claim 1, characterized in that, The failure level for determining no RACH handover based on the timing data includes: If the TAT timer expires, but the T430 and T304 timers have not expired, the failure level is a minor failure. If the TAT timer and T430 timer expire, but the T304 timer has not expired, the failure level is moderate failure. If the TAT timer, T430 timer, or T304 timer expires, the failure level is classified as a severe failure.

3. The hierarchical failure recovery method based on NTN-free RACH handover according to claim 1, characterized in that, When the failure level is a minor failure, the RACH handover failure recovery process includes: The user equipment calculates the TA adjustment value based on the cached satellite ephemeris and its own geographic location, and uses the pre-allocated uplink resources to send a timing advance correction request containing the TA adjustment value to the target cell. The target cell sends a dynamic uplink grant to the target device through the physical downlink control channel. The dynamic uplink grant includes the uplink transmission timing adjusted based on the user equipment TA adjustment value and the new TAT duration. The user equipment performs uplink data transmission based on the dynamic uplink authorization, restarts the TAT timer, and restores normal communication.

4. The hierarchical failure recovery method based on NTN-free RACH handover according to claim 1, characterized in that, When the failure level is moderate, the RACH handover failure recovery process includes: The user equipment sends an incremental update request for satellite parameters to the source cell, carrying the physical cell identifier of the target cell and the cached satellite ephemeris version number. The source cell extracts the satellite ephemeris update fragment of the target satellite from its local cache based on the satellite ephemeris version number and sends it to the user equipment via RRC signaling; User equipment updates the public TA adjustment value and user equipment TA adjustment value by combining the basic parameters of historical cache with incremental data, and completes downlink synchronization of the target cell based on the synchronization signal block of the target satellite and the physical cell identifier of the target cell. User equipment listens to the physical downlink control channel of the target cell, obtains dynamic uplink authorization, sends the first uplink data according to the dynamic uplink authorization, and restarts the T430 timer.

5. The hierarchical failure recovery method based on NTN-free RACH handover according to claim 1, characterized in that, When the failure level is severe failure, the RACH handover failure recovery process includes: User equipment, based on a pre-configured list of co-orbiting satellites, prioritizes searching for alternative beams that have the same physical cell identifier as the target cell; If an available alternative beam exists, the user equipment calculates the TA value using the cached neighbor satellite ephemeris table and sends a RACH-free access request containing the TA value to the alternative cell through pre-allocated uplink resources. If no alternative beam is available, the user equipment triggers the RRC reconstruction process, which searches for and accesses the nearest TN cell based on the pre-configured TN network coverage information.

6. A hierarchical failure recovery device based on NTN-free RACH handover, characterized in that, include: The data acquisition module is configured to acquire timing data from the TAT timer, T430 timer, and T304 timer; The failure stratification module is configured to determine the failure level of no RACH switching based on the timing data. The failure levels include mild failure, moderate failure, and severe failure. The hierarchical recovery module is configured to perform RACH-free handover failure recovery processing based on the failure level.

7. An electronic device, characterized in that, Including processor and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-5.

9. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method described in any one of claims 1-5.

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