A minimal deterministic handover method, system and device suitable for GEO satellite communication

Abstract

This invention discloses a simplified deterministic handover method, system, and apparatus suitable for GEO satellite communication. Addressing the problem of time slot counter loopback caused by the long propagation delay of geostationary orbit (GEO) satellites, this invention introduces absolute timestamp extension based on a simplified scheme based on physical time slot counter degradation. The source base station carries the absolute time and the predicted target cell linear time slot number (next_slot) in the handover command and synchronously notifies the target base station. The UE and the target base station independently increment the count using next_slot as the synchronization anchor point. After tuning, the UE calculates the downlink resource position based on the current linear time slot counter at each time slot boundary and periodically listens for implicit grants. When multiple UEs collide, the target base station selects a winner according to deterministic rules and sends grants only on the winner's downlink resources; the unwinners continue listening, with the worst-case number of listening time slots not exceeding M-1. This invention enables the simplified scheme to support GEO scenarios while maintaining the advantages of low complexity, pure software upgrades, and zero RACH signaling, with a deterministic upper bound on the handover execution interruption time. The technical solution of this invention is also applicable to low Earth orbit (LEO) satellites and terrestrial cellular networks.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically relating to a simplified, low-interruption, deterministic handover method, system, and apparatus for user equipment (UE) between base stations in a deterministic communication system based on Dynamic Security Foundation (DSF), specifically for a geostationary orbit (GEO) satellite scenario. It is particularly suitable for communication systems that rely solely on physical time slot counters and need to handle time slot loopback problems caused by long propagation delays. The technical solution of this invention is also applicable to low Earth orbit (LEO) satellite and terrestrial cellular network scenarios. Background Technology

[0002] The applicant has previously filed several patent applications related to deterministic wireless communication (hereinafter referred to as "preceding patents"), the core mechanisms of which include: zero signaling parameter generation based on Dynamic Security Foundation (DSF) and Protocol Security State Machine (PSSM), two-step deterministic arbitration, and downlink implicit authorization. In the preceding patents, by configuring Rule_ID as Rule A (broadcast clock driven rule), the PSSM state can be degraded to a physical layer system frame number (SFN) and slot number counter, thus obtaining a very simple state machine-free handover scheme (hereinafter referred to as "the simplified scheme"). This simplified scheme does not require maintaining a complex hash chain, and only relies on the shared key K_sec and physical slot synchronization to carry the expected slot number (next_slot) of the target cell in the handover command. After UE tuning, it can directly use the derived resources to transmit and receive data, and the execution interruption time is only the radio frequency retuning time (less than 0.25ms).

[0003] The complete solution in the previous patent (Rule B / C, based on the PSSM state machine) naturally supports scenarios with arbitrary propagation delays, including GEO satellite communication. However, the simplified solution (Rule A degradation), as a special case of the previous patent, was designed for short propagation delay scenarios such as Low Earth Orbit (LEO) satellites and terrestrial cellular networks, where it performs excellently. For geostationary orbit (GEO) satellite scenarios, the simplified solution faces a fundamental challenge: the one-way propagation delay between GEO satellites and the ground is approximately 270ms, while the time slot period of 5G NR depends on the subcarrier spacing (e.g., a time slot length of 0.125ms under a 30kHz subcarrier spacing), and a radio frame (10ms) contains 80 time slots. It takes approximately 270ms for the handover command to be sent from the source base station to the UE, during which time the target cell's time slot counter has looped back more than 27 times. If the source base station still directly sends the current time slot number in the LEO manner, the time slot number received by the UE will be severely outdated, resulting in completely incorrect derived parameters and handover failure.

[0004] In existing technologies, the 3GPP NTN standard (Rel-17 / 18) supports the UE in calculating the frame timing (SFN) of the target cell using GNSS and satellite ephemeris. However, this method is only used for the UE to obtain the broadcast SFN unidirectionally and does not involve time slot synchronization in the handover command, nor does it disclose the mechanism of "the target base station and the UE using the same initial time slot number to independently increment the count". In addition, conventional "timestamp anti-timeout" methods (such as waitTime in RRC messages) are only used for command validity judgment and are not combined with the resource derivation and continuous listening process of the simplified solution.

[0005] Therefore, in order to make the minimalist solution (rule A degradation) applicable to GEO scenarios, an enhancement method needs to be invented to solve the time slot loopback problem while retaining its advantages of low complexity, pure software upgrade, and zero RACH signaling. This invention is proposed for this purpose. Summary of the Invention

[0006] This invention aims to solve the problem of time slot counter loopback caused by long propagation delay in GEO satellite communication. It provides a deterministic handover method, system, and device that extends absolute timestamps based on a simplified scheme (rule A degradation), enabling UEs to achieve sub-millisecond-level deterministic handover of execution interruptions without the need for complex state machines, while maintaining compatibility with existing 5G networks.

[0007] Terminology Definition Dynamic Security Foundation (DSF): refers to a set of cryptographic materials shared by both communicating parties, including at least the shared key K_sec, the initial anchor InitAnchor, and the rule identifier Rule_ID. The DSF is the basis for generating all communication parameters.

[0008] PSSM (Protocol Secure State Machine): This refers to a deterministic state machine independently maintained by both communicating parties. The evolution of its state S(t) depends only on the shared DSF triple (K_sec, InitAnchor, Rule_ID) and a predefined deterministic function (such as a hash chain or counter increment), and is independent of the instantaneous value of the physical clock. Both parties start from the same initial state S(0) and independently compute according to the same Rule_ID, thus maintaining state consistency at any logical moment without the need for real-time signaling interaction.

[0009] Rule A (Broadcast Clock Driven Rule): This refers to a configuration of Rule_ID where the PSSM state S(t) degenerates into a linear slot counter C. This counter can be decomposed into the system frame number (SFN) and the slot number (Slot), i.e., SFN = floor(C / N_slot_per_frame), Slot = C mod N_slot_per_frame, where N_slot_per_frame = 80 (taking a 30kHz subcarrier spacing as an example, a radio frame contains 80 slots; for other subcarrier spacings, N_slot_per_frame changes accordingly). Both communicating parties derive all transmission parameters based on K_sec and C (or the equivalent SFN||Slot) using a cryptographic hash function. This rule forms the basis of the simplified scheme of this invention.

[0010] Implicit downlink granting: This refers to the network side sending a valid downlink signal (which can be an empty frame, an acknowledgment frame, or any decodeable physical layer signal) at the downlink resource location R_d calculated by the UE after completing resource arbitration. The existence of this signal and its successful decoding by the UE constitutes granting the UE the right to use the paired uplink resource R_u, without requiring any explicit granting signaling bits.

[0011] Synchronization Anchor Point (next_slot): This refers to the absolute linear timeslot number (including SFN and Slot information) that the target base station should be in when the UE is expected to receive the handover command, calculated by the source base station based on the propagation delay estimate. This value is simultaneously sent to the UE and notified to the target base station through the Xn interface, serving as the initial value for the timeslot counters of both parties, ensuring that both parties independently increment the count from the same reference.

[0012] Total number of resource units M: This refers to the total number of physical resource units used by the target base station for this service flow. Each resource unit corresponds to a time-domain and frequency-domain location (e.g., a specific combination of OFDM symbols and physical resource blocks (PRBs) within a time slot). M determines the modulus of the hash derivation modulo operation, i.e., Resource_Index = HMAC - SHA256(...) mod M. The larger M is, the lower the probability of resource collisions, but the larger the worst-case waiting time slots for arbitration (not exceeding M-1).

[0013] Two-step deterministic arbitration: When multiple UEs calculate the same downlink resource location in the same time slot, the target base station employs a two-step conflict resolution method. Step 1: Identify all colliding UEs and select a winner based on preset deterministic rules (such as priority and UE_ID size). Step 2: Check whether the winner's intended resource is available at the corresponding time. After successful arbitration, the target base station only sends implicit grants on the winner's downlink resources. UEs that do not win continue to listen in subsequent time slots. This mechanism ensures that, in the worst case, the number of time slots a UE needs to listen in does not exceed M-1. The arbitration mechanism of this invention is the same as that in the previous patent, but it is applied to the GEO simplified handover scenario.

[0014] Technical solution This invention provides a simplified deterministic handover method suitable for GEO satellite communications, comprising the following steps: Step S1: Source base station prepares handover command The source base station (gNB-S) determines whether the UE needs to hand over to the target base station (gNB-T) based on the measurement report reported by the UE or network decisions. The source base station obtains the following information: - The current service time reference of the target base station (such as SFN, Slot) can be obtained through the Xn interface or the core network; - The total number of resource units M used by the target base station for this service flow and other localized communication parameters (such as resource grid offset). - Propagation delay estimate T_prop_est (e.g., calculated based on UE location and satellite ephemeris, or estimated from historical TA values); - An absolute time reference (such as GNSS time), which can be synchronized between base stations or maintained independently by each base station.

[0015] The source base station calculates the expected time when the UE will receive the handover command, T_cmd_arrival_est = now + T_prop_est, and calculates the target base station's absolute linear timeslot number corresponding to that time. next_slot = f_target(T_cmd_arrival_est) Here, `f_target` is a function that maps absolute time to the target base station's linear timeslot number. The target base station broadcasts its current system frame number `SFN_ref`, timeslot number `Slot_ref`, and corresponding absolute time reference point `T_ref` (e.g., GNSS time) via a System Information Block (SIB). After receiving this information, the UE constructs the mapping function by combining the frame structure parameters (number of timeslots per frame `N_slot_per_frame`, timeslot length `T_slot`): for any absolute time `T`, the corresponding linear timeslot number `C` = (`SFN_ref` × `N_slot_per_frame` + `Slot_ref`) + `floor((T - T_ref) / T_slot)`. The source base station and the UE use the same mapping function to calculate `next_slot`.

[0016] The source base station constructs a handover command (RRCReconfiguration message), which includes: - Localized communication parameters of the target base station, including the total number of resource units M, resource grid offset, etc.; - The next_slot value (a 32-bit integer, with the high 22 bits representing SFN and the low 10 bits representing Slot); - Absolute timestamp T_abs: This is the absolute time (such as GNSS time, with an accuracy better than one time slot step T_slot) used by the source base station when sending the handover command, serving as the benchmark for UE verification time slot calculation. Preferably, the absolute timestamp is provided by GNSS, with an accuracy better than 1μs, much smaller than the minimum time slot step.

[0017] Step S2: UE and network side synchronize time slot counter initial value After receiving the handover command, the UE extracts parameters such as T_abs, next_slot, and M. The UE calculates the current absolute time T_now_abs based on its own maintained absolute time (e.g., GNSS receiver) or local clock (synchronized with the network). If |T_now_abs - T_abs| exceeds a preset threshold (e.g., 50ms), the handover command is deemed outdated, triggering a retransmission or fallback procedure. Otherwise, the UE uses next_slot as the synchronization anchor value for the target cell's time slot counter (similar to InitAnchor in DSF, but degenerated into a specific linear time slot number) and begins incrementing T_slot periodically (the time slot step size can be configured as a single time slot or L time slots, where L is a positive integer, pre-configured by the network and notified to the UE; for example, L=2,4,8, used to reduce UE calculation power consumption).

[0018] Crucially, the target base station (gNB-T) also uses the same `next_slot` as the synchronization anchor value for the UE's slot counter. This value is generated by the target base station and fed back to the source base station during the handover preparation phase, or calculated by the source base station and notified to the target base station via the Xn interface. The target base station initializes the UE's virtual slot counter accordingly and increments it synchronously with the UE's local counter (using the same step size). Both sides start from the same initial value and evolve independently with the same step size, thereby ensuring that at each slot boundary, the downlink resource location `Resource_DL` and uplink resource location `Resource_UL` calculated by the UE and the network side are completely consistent. This "bidirectional synchronization anchor" mechanism is the core feature that distinguishes this invention from existing GNSS-assisted schemes (where only the UE obtains the SFN unidirectionally).

[0019] Step S3: UE performs radio frequency handover The UE completes radio frequency retuning to the target cell frequency within the time window specified by the handover command (e.g., 5ms to 10ms after receiving the command). This step does not rely on any signaling interaction and is controlled solely by the UE's local timer.

[0020] Step S4: The UE calculates the downlink resource location at each time slot boundary and periodically listens for implicit grants. After tuning, at each slot boundary (i.e., each time step unit), the UE calculates the physical location of the downlink listening resource using a cryptographic hash function (e.g., HMAC-SHA256), based on the shared key K_sec and the current linear slot counter value C (provided by the locally maintained slot counter, which can be decomposed into the system frame number SFN = floor(C / N_slot_per_frame) and the slot number Slot = C mod N_slot_per_frame). Resource_DL = HMAC-SHA256(K_sec, SFN || Slot || "DL") mod M Where M represents the total number of resource elements in the target cell used for this service flow. This resource location corresponds to a specific physical resource block (PRB) and OFDM symbol within that time slot in the 5G radio frame. The UE does not require any downlink control information (DCI) to indicate this resource location; it is determined entirely by local calculation.

[0021] The UE attempts to receive a signal on the physical downlink resources corresponding to the time slot. If a valid downlink signal is successfully decoded (this signal can be an empty frame, an acknowledgment frame, or any identifiable physical layer signal), implicit authorization is determined; otherwise, the UE continues to repeat the above calculation and listening process at the next time slot boundary. The UE can enter a low-power sleep state during this period, only waking up briefly at each time slot boundary to perform a listening operation.

[0022] Step S5: Two-step deterministic arbitration in multi-user scenarios When multiple UEs simultaneously handover to the same target cell, and their calculated Resource_DL values ​​are identical in a certain time slot, the target base station will detect a collision. At this point, the target base station performs a two-step deterministic arbitration: it selects a winner from the collision set based on preset deterministic rules (e.g., selecting the UE with the smallest identifier, the highest priority, or an order based on hash values), and sends an implicit grant only on the winner's downlink Resource_DL. Unsuccessful UEs will not receive any signal in that time slot (or will receive a silence indication), and they will continue listening in the next time slot. Since the total number of resource units is M, in the worst case, a UE may need to continuously listen for M-1 time slots to win (because each time slot can exclude at most one collider). The detailed implementation of this arbitration mechanism is the same as in the previous patent; this invention applies it to the GEO simplified handover scenario.

[0023] Step S6: UE sends uplink data Once the UE successfully receives implicit grant on Resource_DL in a certain time slot, the UE immediately calculates the paired uplink resource location based on the same current linear time slot counter C: Resource_UL = HMAC-SHA256(K_sec, SFN || Slot || "UL") mod M The UE transmits uplink data at the corresponding uplink transmission time in that time slot (following the frame timing of 5G NR, the uplink transmission time has a fixed time offset from the downlink reception time, for example, after downlink reception, it undergoes a processing delay by the UE before transmission). Throughout the entire process, the UE does not need to send any random access preamble or scheduling request (SR), nor does it need to receive TA update commands.

[0024] Step S7: Time Slot Synchronization Calibration for GEO Scene Due to the 270ms delay in GEO propagation, the prediction of next_slot may have an error of several milliseconds. To absorb this error, the UE can periodically check whether its own time slot counter is consistent with the SFN broadcast by the target cell during the listening process. Specifically, the UE can listen to the broadcast channel of the target cell (such as SIB1), extract the current SFN, and compare it with the high bit (SFN part) of its local counter. If the deviation is found to exceed one radio frame (10ms), the UE recalibrates its local counter according to the broadcast SFN, using the calibration formula: C_new = (SFN_broadcast × N_slot_per_frame) + (C_old mod N_slot_per_frame). This calibration process does not rely on additional signaling interaction.

[0025] Linear slot counter overflow handling: Since the maximum value of the 32-bit linear slot counter is 4,294,967,295, corresponding to approximately 6.8 days (in 0.125ms steps), when it exceeds this range, the bit width can be extended (e.g., to 64 bits) or the count value can be modulo (SFN period × N_slot_per_frame) without affecting the consistency of resource calculation. This invention does not limit the specific overflow handling method.

[0026] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: 1. Solving the GEO timeslot loopback problem: By introducing absolute timestamps and bidirectional synchronization anchors (the UE and the target base station use the same independent incrementing next_slot count), the loopback error caused by long propagation delays is avoided. Unlike existing GNSS-assisted schemes (where only the UE obtains the SFN unidirectionally), the bidirectional anchor mechanism of this invention ensures the consistency of resource calculations between the two parties.

[0027] 2. Maintaining the advantages of a simplified solution: No complex PSSM state machine or hash chain needs to be supported by the UE; only physical time slot counters and HMAC calculations are required, ensuring compatibility with existing 5G terminal software upgrades. Downlink resource locations are determined locally, eliminating the need for DCI scheduling.

[0028] 3. Deterministic Latency Guarantee: The UE periodically calculates and listens for downlink resources at each time slot boundary until it receives implicit authorization. Through two-step arbitration, the number of time slots the UE needs to listen for in the worst case does not exceed M-1. Including the RF retuning time, the total execution interruption time has a strict mathematical upper bound, decoupled from the 270ms propagation delay of GEO (the propagation delay occurs outside the interruption window).

[0029] 4. Complementary to previous patent systems: This invention specifically enhances the minimalist solution (rule A degradation) in the GEO scenario, clarifying its scope of protection. The complete solutions (rules B / C) in previous patents already support GEO, while this invention provides a supplementary solution for scenarios where a minimalist implementation is desired.

[0030] 5. Backward compatibility: The technical solution of this invention is not only applicable to GEO satellite scenarios, but also to low Earth orbit (LEO) satellites and terrestrial cellular networks. In short propagation delay scenarios, the verification threshold of the absolute timestamp can be relaxed accordingly without affecting the handover success rate. Attached Figure Description

[0031] Figure 1 This is a signaling flowchart for the simplified deterministic handover in the GEO scenario described in this invention.

[0032] Figure 2 A flowchart for initializing the UE-side time slot counter and verifying the absolute timestamp.

[0033] Figure 3 A flowchart for calculating downlink resources for the UE at each time slot boundary and periodically monitoring them. Detailed Implementation

[0034] The invention will now be described in detail with reference to a specific example.

[0035] Scenario: A GEO satellite (target base station gNB-T) covers the equator, and the UE is located at a fixed position on the ground. One-way propagation delay is 270ms. System parameters: subcarrier spacing 30kHz, time slot step T_slot = 0.125ms, number of time slots per frame N_slot_per_frame = 80, total number of resource units M = 50, radio frequency retuning time T_rf = 0.25ms. The source base station gNB-S and gNB-T are connected via a terrestrial core network; both are equipped with GNSS receivers, and time synchronization accuracy is better than 1 microsecond.

[0036] Step 1: Trigger the switch The UE reports a measurement report, and gNB-S decides to handover to gNB-T. gNB-S requests handover preparation from gNB-T via the Xn interface, obtaining gNB-T's localized communication parameters (including M=50, resource grid offset, etc.) and the current SFN and Slot (e.g., SFN=1000, Slot=5). Simultaneously, gNB-T informs the UE that it will use the UE's next_slot as the synchronization anchor point and promises that both parties will independently increment the count from this anchor point.

[0037] Step 2: Calculate next_slot and T_abs The gNB-S obtains the current absolute time (GNSS) T_now_abs = 2025-04-05 12:00:00.000. The estimated propagation delay T_prop_est = 270ms, therefore the expected time the UE receives the command is T_arrival_abs = T_now_abs + 270ms = 2025-04-05 12:00:00.270. Based on the gNB-T frame structure, the gNB-S uses the f_target function to calculate the gNB-T linear slot number corresponding to T_arrival_abs. Assuming that the gNB-T's SFN = 1000 and Slot = 5 at T_now_abs, the linear slot number C_now = 1000 × 80 + 5 = 80,005. After 270ms (2160 time slots), C_next = 80,005 + 2160 = 82,165. Decomposing this, we get SFN = floor(82,165 / 80) = 1027, and Slot = 82,165 mod 80 = 5. Therefore, next_slot = 82,165 (or encoded as the high 22 bits SFN = 1027, and the low 10 bits Slot = 5). gNB-S records T_abs = T_now_abs (with a precision better than 0.125ms). gNB-S notifies gNB-T of next_slot via the Xn interface. Based on this, gNB-T initializes the UE's virtual time slot counter to 82,165, and agrees with the UE to independently increment it from this point onwards.

[0038] Step 3: Issue the switching command gNB-S sends a handover command to the UE via an RRCReconfiguration message, which carries next_slot (82,165), T_abs, and localized communication parameters (including M=50).

[0039] Step 4: The UE processes the handover command and initializes the counter. After receiving the command, the UE reads its own GNSS time T_rcv_abs = 2025-04-05 12:00:00.272 (the actual arrival time may vary slightly due to processing delays). The UE calculates Δt = T_rcv_abs - T_abs = 272ms, which differs from the estimated value of 270ms by 2ms, within the allowable range (the threshold can be set to 10ms). The UE loads next_slot = 82,165 as the synchronization anchor point into the slot counter and begins incrementing it at a period of 0.125ms.

[0040] Step 5: UE Tuning and Periodic Monitoring The UE completes radio frequency retuning within the time window specified by the handover command (e.g., 5ms to 6ms after receiving the command). Afterward, the UE performs the following operations at each time slot boundary: - Read the current linear time slot counter C (e.g., initially 82,165, then 82,166, 82,167, ...), decompose it into SFN = floor(C / 80), Slot = C mod 80.

[0041] - Calculate Resource_DL = HMAC-SHA256(K_sec, SFN || Slot || "DL") mod 50.

[0042] - Attempt to receive a signal on the downlink resources of the corresponding time slot.

[0043] Since the target base station gNB-T has also initialized the virtual slot counter for the same UE to 82,165 and incremented it synchronously, and has pre-configured the UE's DSF context (shared key K_sec and rule A), the Resource_DL calculated by both parties in each slot is completely consistent. Assuming that two other UEs (UE2 and UE3) simultaneously switch to the same target cell, and their calculated Resource_DL is the same as the current UE's in some slots, the target base station performs a two-step deterministic arbitration. According to preset rules (e.g., the smallest UE_ID wins), assuming the current UE wins, gNB-T sends a downlink implicit grant on the winner's Resource_DL. The current UE successfully receives the grant in the 8th slot (C = 82,165 + 7 = 82,172, corresponding to SFN = 1027, Slot = 12). In the worst case, if the current UE does not win, it will need to listen for a maximum of M-1 = 49 slots (approximately 6.125 ms).

[0044] Step 6: UE sends uplink data The UE calculates Resource_UL = HMAC-SHA256(K_sec, SFN|| Slot || "UL") mod 50 based on the current linear slot counter C, and transmits data during the uplink transmission time of that slot. The total execution interruption time is T_rf + 8 × T_slot = 0.25ms + 1.0ms = 1.25ms, with a worst-case time of 0.25ms + 49*0.125ms = 6.375ms, which is far better than the hundreds of milliseconds of traditional GEO handover.

[0045] Step 7: Exception Handling If the UE detects a prolonged period (e.g., 100ms) without receiving authorization during the listening process, it determines that a time slot calculation error may have caused a loss of synchronization. In this case, the UE actively listens for the broadcast SFN (SIB1) of the target cell, obtains the actual SFN, and compares it with the SFN derived from its local counter. If the deviation exceeds one radio frame (10ms), the UE recalibrates its local counter based on the broadcast SFN using the calibration formula: C_new = (SFN_broadcast × N_slot_per_frame) + (C_old mod N_slot_per_frame), and continues listening. If the UE still fails, it falls back to the traditional RACH procedure.

Claims

1. A simplified deterministic handover method suitable for GEO satellite communications, characterized in that, include: The source base station acquires the target base station's localized communication parameters and current timeslot information, wherein the localized communication parameters include at least the total number of resource units M; The source base station calculates the expected time when the UE will receive the handover command based on the propagation delay estimate, and determines the target base station linear timeslot number next_slot corresponding to that time. The source base station sends the absolute timestamp T_abs and the next_slot to the UE in the handover command, and notifies the target base station of the next_slot through the inter-base station interface; After receiving the handover command, the UE uses T_abs to verify the freshness of the command and initializes the local time slot counter with next_slot as the synchronization anchor point; the target base station initializes the UE's virtual time slot counter with the same next_slot. The UE and the target base station start from the same initial linear timeslot number and independently increment the count with the same step size; After the UE tunes to the target cell, it calculates the downlink resource location based on the value of the current linear time slot counter at each time slot boundary, and periodically listens for implicit grants on the physical downlink resources corresponding to that time slot. When multiple UEs calculate the same downlink resource location in the same time slot, the target base station selects the winner according to deterministic rules and sends implicit authorization only on the downlink resources of the winner; After receiving the implicit grant, the UE calculates the paired uplink resource location and sends uplink data.

2. The method according to claim 1, characterized in that, The absolute timestamp T_abs is GNSS time or a unified absolute time maintained by the network side, and its accuracy is better than a time slot step.

3. The method according to claim 1, characterized in that, The estimated propagation delay is calculated based on the UE's geographical location and satellite ephemeris, or estimated based on historical timing advance (TA) values.

4. The method according to claim 1, characterized in that, The increment step size of the time slot counter can be configured as a single time slot or L time slots, where L is a positive integer, and is pre-configured by the network and notified to the UE.

5. The method according to claim 1, characterized in that, The linear slot counter can be decomposed into system frame number SFN = floor(C / N_slot_per_frame) and slot number Slot = C mod N_slot_per_frame, where C is the value of the linear slot counter and N_slot_per_frame is the number of slots contained in a radio frame, which depends on the subcarrier spacing.

6. The method according to claim 5, characterized in that, The downlink resource location is calculated using the following formula: Resource_DL = HMAC-SHA256(K_sec, SFN || Slot || "DL") mod M, where K_sec is the key shared between the UE and the network.

7. The method according to claim 6, characterized in that, The uplink resource location is calculated using the following formula: Resource_UL = HMAC-SHA256(K_sec, SFN || Slot || "UL") mod M.

8. The method according to claim 1, characterized in that, The downlink resource location and uplink resource location correspond to specific physical resource blocks (PRBs) and OFDM symbols within the time slot of the 5G radio frame, and do not require downlink control information (DCI) indication.

9. The method according to claim 1, characterized in that, If the UE does not receive implicit authorization for a long time during the listening process, it will calibrate the local time slot counter by listening to the broadcast system frame number (SFN) of the target cell.

10. The method according to claim 1, characterized in that, The deterministic rule for selecting the winner is one or more combinations of comparing UE identifier (UE_ID) size, service priority, or order based on hash value.

11. The method according to claim 1, characterized in that, The total number of resource units M determines that the number of time slots the UE needs to listen to in the worst case does not exceed M-1.

12. A simplified deterministic handover system suitable for GEO satellite communication, comprising a source base station, a target base station, and user equipment, characterized in that, The source base station is configured to perform the method according to any one of claims 1 to 11; the target base station is configured to initialize a virtual time slot counter with the same next_slot as the UE, and perform the winner selection and implicit grant transmission; the user equipment is configured to receive and process a handover command containing an absolute timestamp and next_slot, and calculate the downlink resource location based on a linear time slot counter at each time slot boundary and periodically listen for implicit grant.

13. A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method of any one of claims 1 to 11.

14. A user equipment comprising a processor, a memory, a transceiver, and a GNSS receiver, characterized in that, The processor executes the program in the memory to implement the steps on the UE side of the method according to any one of claims 1 to 11.

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