A low earth orbit communication satellite handover method

Abstract

The application discloses a kind of low-orbit communication satellite switching methods, belong to satellite communication technical field, the application discards the traditional thought of "terminal active search, measure target satellite", by the downlink and uplink synchronization state information of target satellite in real time acquisition by current satellite through inter-satellite link (ISL), this synchronization state information (non-ephemeris, orbit parameter) is directly issued to terminal;Terminal receives only the signal of current satellite throughout, without receiving, measuring, synchronizing any signal of target satellite, only executes radio frequency point switching when switching, that is, according to the synchronization state information issued by current satellite, directly demodulates the service signal of target satellite, completely skips all time-consuming steps such as cell search, synchronization, random access, and realizes instantaneous switching.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a method for switching low-Earth orbit communication satellites. Background Technology

[0002] Low Earth Orbit (LEO) satellite communication systems offer advantages such as low latency, wide coverage, and high bandwidth, making them a core component of 5G NTN (non-terrestrial network) and widely used in scenarios such as vehicle-mounted systems, portable terminals, and communications in remote areas. LEO satellites orbit the Earth at high speeds (approximately 7.8 km / s), and the link duration between terminals and satellites is short (typically 5-15 minutes). Therefore, satellite handover (i.e., the terminal switching from a serving satellite to a target satellite) is a key technology for ensuring communication continuity. Figure 1 The image shows a demonstration of satellite handover.

[0003] The core logic of existing low-Earth orbit satellite inter-frequency handover (where the serving satellite and the target satellite have different carrier frequencies) is as follows: After the terminal detects a decline in the signal quality of the serving satellite, it triggers the handover process. First, it disconnects from the serving satellite, then switches to the target satellite frequency through radio frequency tuning. Subsequently, it performs a series of steps such as cell search, synchronization (PSS / SSS detection, frame synchronization), random access (PRACH), and RRC reconfiguration, and finally completes access to the target satellite and restores service transmission.

[0004] To shorten handover latency, existing technologies have explored "serving satellite-assisted handover." The core idea is that the serving satellite provides the terminal with some auxiliary information about the target satellite to reduce the terminal's search and synchronization time. However, this still doesn't overcome the limitations of the traditional handover process. The mainstream industry approach is "PCI-invariant handover": solutions such as those applied for by China Mobile (WO / 2025 / 031027), Quectel Wireless Solutions (WO / 2025 / 107140), and Ericsson (CN121713409) all use network-based auxiliary information (SSB index, timing difference, etc.) to help the terminal locate the target satellite's synchronization signal. However, the essence of these solutions is still "telling the terminal where to find the target satellite's signal," and the terminal still needs to perform the target satellite's SSB search and downlink synchronization process.

[0005] Existing satellite frequency handover technologies (including those assisted by serving satellites) have the following core shortcomings, failing to meet the requirements of low-Earth orbit satellite communication for "instantaneous handover, low power consumption, single hardware, and full-scenario operation":

[0006] Defect 1: The handover latency is still relatively high, failing to meet the requirement of instantaneous handover. In existing technologies, even with the assistance of serving satellites, the terminal still needs to perform the "RF adjustment + cell search + synchronization + random access" process, with handover latency typically ranging from 100 to 1000 ms. This cannot meet the latency-sensitive service requirements of vehicle networking, real-time communication, and other applications, and can easily lead to service interruptions and data packet loss.

[0007] Defect 2: Terminal reliance on ephemeris leads to high complexity. In existing service satellite assistance technologies, the service satellite only forwards the target satellite's ephemeris, orbital parameters, or Doppler model to the terminal, which then needs to calculate the target satellite's synchronization parameters (time offset, frequency offset, etc.) itself.

[0008] Defect 3: Obtaining the signal frame boundary of the target satellite and the downlink and uplink timing information requires the terminal to perform neighbor cell measurements, which greatly increases the computing power burden on the terminal and increases the complexity of the solution.

[0009] Defect 4: Neighbor cell measurements also place higher demands on the antenna; the phased array needs to support simultaneous tracking and receiving signals from multiple satellite links. Parabolic antennas, on the other hand, require at least two to be deployed. This increased technical difficulty leads to higher costs. Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of this invention is to provide a low-Earth orbit communication satellite switching method, so as to at least partially solve the above-mentioned problems.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] In a first aspect, the present invention provides a method for switching low-Earth orbit communication satellites, the method being applied to a terminal side, the method comprising the following steps:

[0013] The terminal receives downlink data from the current satellite in real time and determines whether it needs to switch the service transmission to the target satellite. The downlink data includes synchronization status information that the current satellite obtains from the target satellite in real time through the inter-satellite link.

[0014] When it is necessary to switch the service transmission to the target satellite, the terminal disconnects from the current satellite, demodulates the downlink signal of the target satellite using the latest received synchronization status information, and sends uplink services, thereby switching the service transmission to the target satellite. The synchronization status information includes UTC time, uplink carrier frequency of the target satellite, downlink carrier frequency of the target satellite, time offset of the target satellite, frequency offset of the target satellite, physical cell ID of the target satellite, common configuration of the target satellite cell, and preset private configuration of the target satellite cell.

[0015] In some preferred embodiments, the terminal receives downlink data transmitted by the current satellite in real time and then performs local caching.

[0016] In some preferred embodiments, the carrier frequencies of the current satellite and the target satellite are different, and during switching, the terminal controls the radio frequency module to switch frequencies.

[0017] In some preferred embodiments, post-calibration is also included. When the service transmission service switches from the current satellite to the target satellite, the terminal further fine-tunes the cached synchronization status information based on the downlink SSB signal of the target satellite to improve demodulation reliability.

[0018] In some preferred embodiments, a pre-calculation is also included. Before switching service transmission, the terminal performs interpolation calculation based on the change in frame boundary offset and calculates the frame boundary adjustment value that matches the current time in combination with its own real-time time to ensure that the switching time parameters are accurate.

[0019] In some preferred embodiments, when the terminal detects that the signal quality of the current satellite meets the switching conditions or when the terminal receives a switching instruction from the current satellite, the terminal switches the service transmission service to the target satellite.

[0020] Secondly, the present invention also provides a method for switching low-Earth orbit communication satellites, the method being applied to the satellite side, the method comprising the following steps:

[0021] The current satellite receives synchronization status information sent by the target satellite via inter-satellite link;

[0022] The current satellite encapsulates the target satellite's synchronization status information into downlink data and sends it to the currently accessed terminal in real time. This enables the terminal to demodulate the target satellite's downlink signal and send uplink services when switching satellites, using the latest received synchronization status information. This allows the terminal's service transmission to switch from the current satellite to the target satellite. The synchronization status information includes UTC time, the target satellite's uplink carrier frequency, the target satellite's downlink carrier frequency, the target satellite's time offset, the target satellite's frequency offset, the target satellite's physical cell ID, the target satellite cell's common configuration, and the target satellite cell's pre-configured dedicated configuration.

[0023] In some preferred embodiments, the current satellite transmits downlink data in period Y, and before the current satellite transmits downlink data, it is also necessary to deduce the change in the frame boundary offset of the target satellite, with a deduction duration of X, where X < Y.

[0024] In some preferred embodiments, the current satellite also transmits its own synchronization status information in real time to the satellite ahead of it in its direction of travel via an inter-satellite link.

[0025] By adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0026] Advantage 1: Terminal handover latency reaches the physical limit, achieving instantaneous handover. The method of this invention completely skips all time-consuming steps such as cell search, synchronization, and random access. The handover time is only equal to the radio frequency switching time, which is far lower than the 50-100ms of the existing technology. It can fully meet the needs of latency-sensitive services and achieve low latency, zero interruption, and no packet loss.

[0027] Advantage 2: Terminal switching requires no ephemeris data or ground-based dependencies, offering strong versatility. The terminal requires no ephemeris data, orbital parameters, or positioning information, and requires no ground gateway relay. It can complete the switching solely based on the synchronization status information of the target satellite directly transmitted from the current satellite; suitable for all low-Earth orbit satellite frequency switching scenarios.

[0028] Advantage 3: Low terminal complexity and controllable hardware costs. The terminal adopts a single antenna and single radio frequency architecture, receiving only the signal from the current satellite throughout the entire process. It does not require dual-path processing or additional measurement modules, resulting in low computing power requirements and significantly reduced power consumption. It can be adapted to various low-cost devices such as portable terminals and vehicle-mounted terminals.

[0029] Advantage 4: No satellite modification required, excellent compatibility. The target satellite does not require additional broadcast auxiliary pilots, frame alignment, or simultaneous data broadcasting. It only needs to feedback its own synchronization status information through inter-satellite links, and can be directly compatible with all existing normally operating low-Earth orbit satellites without the need for additional on-board modification costs.

[0030] Advantage 5: Low bandwidth consumption and no interference. The current satellite only sends out a few dozen bytes of synchronization status information and does not forward any signals from the target satellite. This consumes very little bandwidth, does not interfere with the current satellite's own service signals, and does not affect communication quality. Attached Figure Description

[0031] Figure 1 This is a schematic diagram demonstrating satellite handover.

[0032] Figure 2 This is a schematic diagram of the satellite switching process in this invention. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] This invention provides a method for handover of low-Earth orbit communication satellites. This method is applied to the terminal side, and the terminal may include, but is not limited to, at least one of the following: user equipment, network equipment, etc. The user equipment may include, but is not limited to, computers, smartphones, personal digital assistants (PDAs), etc. The network equipment may include, but is not limited to, a single network server, a server group consisting of multiple network servers, or a cloud based on cloud computing consisting of a large number of computers or network servers. Cloud computing is a type of distributed computing, consisting of a super virtual computer composed of a group of loosely coupled computers. This embodiment does not limit the specific type of terminal.

[0036] like Figure 2 The diagram shows a flowchart of a low-orbit communication satellite switching method provided by an embodiment of the present invention. This method is used to switch the terminal's service from the current satellite to the target satellite.

[0037] The current satellite (i.e., the serving satellite) establishes real-time communication with the target satellite via an inter-satellite link (ISL). The current satellite also receives synchronization status information from the target satellite in real-time via the ISL. This synchronization status information includes UTC time, the target satellite's uplink carrier frequency, downlink carrier frequency, time offset, frequency offset, physical cell ID, common configuration, and pre-configured dedicated configuration. The target satellite's time offset is based on the current satellite's offset and includes downlink and uplink frame boundary and frame number offsets. Similarly, the target satellite's frequency offset is also based on the current satellite's offset and includes uplink and downlink Doppler frequency offsets. The pre-configured dedicated configuration includes all other necessary access configurations, such as C-RNTI.

[0038] Except for the short period of frame boundary offset, the periods of other information are relatively long. This long-period information can be configured to be transmitted only when there are changes. The target satellite can also acquire the terminal's location information, and the target satellite is a subsequent satellite used to provide service transmission to the terminal.

[0039] Before switching, the terminal tracks the frequency point f1 of the current satellite and demodulates the service signal of the current satellite normally, and the terminal performs service transmission services with the current satellite.

[0040] Meanwhile, the terminal also receives downlink data from the current satellite in real time. This downlink data includes synchronization status information that the current satellite obtains from the target satellite in real time via the inter-satellite link. For example, the current satellite encapsulates the synchronization status information received from the target satellite into downlink shared channel data to form downlink data, and then sends the downlink data to the currently accessed terminal in real time. Considering the link latency (one-way propagation latency is about 1.7-6.7ms, and the actual end-to-end latency is usually 20-50ms), the current satellite also needs to estimate the change in the frame boundary offset of the target satellite before sending downlink data. The estimation time is X (usually 20-50ms), and the period of the current satellite sending downlink data is Y (Y > X).

[0041] Typically, after receiving downlink data (containing synchronization status information of the target satellite) from the current satellite in real time, the terminal performs local caching, for example, always caching the most recently received one.

[0042] At the same time, the terminal will also determine whether it is necessary to switch the service transmission service to the target satellite. For example, the terminal will only perform satellite switching when it detects that the signal quality of the current satellite meets the switching conditions (such as RSRP being lower than a set threshold) or when the terminal receives a switching instruction from the current satellite.

[0043] The terminal performs an instantaneous handover, specifically: the terminal immediately disconnects from the current satellite and controls the radio frequency module to switch from the current satellite's frequency point f1 to the target satellite's frequency point f2. Subsequently, the terminal calls the latest received synchronization status information in the cache. Since the synchronization status information is a "finished product" real-time parameter, the terminal does not need to perform secondary calculations or perform steps such as cell search, PSS / SSS synchronization, and PRACH random access. It can directly demodulate the downlink signal of the target satellite and send uplink services, thus switching the terminal's service transmission service to the target satellite.

[0044] Before the terminal determines that satellite handover is required and before the handover is executed, it also includes pre-preparation calculations, namely: the terminal performs interpolation calculations based on the change in frame boundary offset, and calculates the frame boundary adjustment value that matches the current time in combination with its own real-time time, so as to ensure that the handover timing parameters are accurate.

[0045] After the terminal completes the satellite handover, it also performs post-calibration, which involves fine-tuning the synchronization status information cached by the terminal based on the downlink SSB signal of the target satellite to improve demodulation reliability. This fine-tuning process does not affect the continuity of service transmission. Similarly, uplink fine-tuning is performed using MAC CE.

[0046] Compared with the prior art, the method provided by the embodiments of the present invention has the following outstanding advantages:

[0047] Advantage 1: Terminal handover latency reaches the physical limit, achieving instantaneous handover. The method of this invention completely skips all time-consuming steps such as cell search, synchronization, and random access. The handover time is only equal to the radio frequency switching time, which is far lower than the 50-100ms of the existing technology. It can fully meet the needs of latency-sensitive services and achieve low latency, zero interruption, and no packet loss.

[0048] Advantage 2: Terminal switching requires no ephemeris data or ground-based dependencies, offering strong versatility. The terminal requires no ephemeris data, orbital parameters, or positioning information, and requires no ground gateway relay. It can complete the switching solely based on the synchronization status information of the target satellite directly transmitted from the current satellite; suitable for all low-Earth orbit satellite frequency switching scenarios.

[0049] Advantage 3: Low terminal complexity and controllable hardware costs. The terminal adopts a single antenna and single radio frequency architecture, receiving only the signal from the current satellite throughout the entire process. It does not require dual-path processing or additional measurement modules, resulting in low computing power requirements and significantly reduced power consumption. It can be adapted to various low-cost devices such as portable terminals and vehicle-mounted terminals.

[0050] Advantage 4: No satellite modification required, excellent compatibility. The target satellite does not require additional broadcast auxiliary pilots, frame alignment, or simultaneous data broadcasting. It only needs to feedback its own synchronization status information through inter-satellite links, and can be directly compatible with all existing normally operating low-Earth orbit satellites without the need for additional on-board modification costs.

[0051] Advantage 5: Low bandwidth consumption and no interference. The current satellite only sends out a few dozen bytes of synchronization status information and does not forward any signals from the target satellite. This consumes very little bandwidth, does not interfere with the current satellite's own service signals, and does not affect communication quality.

[0052] Example 2

[0053] This invention also provides a method for switching low-Earth orbit communication satellites. This method is applied to the satellite side and includes the following steps:

[0054] The current satellite receives synchronization status information sent by the target satellite via inter-satellite link;

[0055] The current satellite encapsulates the synchronization status information of the target satellite into downlink data and sends it to the currently accessed terminal in real time. This enables the terminal to demodulate the downlink signal of the target satellite and send uplink services when switching satellites, using the latest received synchronization status information, thus switching the terminal's service transmission from the current satellite to the target satellite.

[0056] The current satellite transmits downlink data in period Y. Before the current satellite transmits downlink data, it is necessary to deduce the change in the frame boundary offset of the target satellite. The deduction time is X, where X < Y.

[0057] The synchronization status information specifically includes: the uplink and downlink carrier frequencies of the target satellite, the transmission time (i.e., aligned with GPS time), the time-frequency offset based on the cell corresponding to the transmission time (including downlink and uplink frame boundary offsets, frame number offsets, and Doppler frequency offsets), the cell ID, common configurations, and preset dedicated configurations. Except for the frame boundary offset, which has a relatively short period, the other information has longer periods. This long-period information can be configured to be transmitted only when changes occur. The target satellite can also acquire the terminal's location information, and it is a subsequent satellite used to provide service transmission to the terminal.

[0058] The current satellite refers to the satellite that the terminal has connected to, and the target satellite refers to the satellite that the terminal will connect to in the future. It is easy to understand that the current satellite is also the target satellite relative to the satellite that the terminal previously connected to but has disconnected. Therefore, the functional positions of the current satellite and the target satellite can be interchanged. Thus, the current satellite also sends its own synchronization status information to the satellite ahead of it in real time through the inter-satellite link.

[0059] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for switching low-Earth orbit communication satellites, the method being applied to the terminal side, characterized in that, The method includes the following steps: The terminal receives downlink data from the current satellite in real time and determines whether it needs to switch the service transmission to the target satellite. The downlink data includes synchronization status information that the current satellite obtains from the target satellite in real time through the inter-satellite link. When it is necessary to switch the service transmission to the target satellite, the terminal disconnects from the current satellite, demodulates the downlink signal of the target satellite using the latest received synchronization status information, and sends uplink services, thereby switching the service transmission to the target satellite. The synchronization status information includes UTC time, uplink carrier frequency of the target satellite, downlink carrier frequency of the target satellite, time offset of the target satellite, frequency offset of the target satellite, physical cell ID of the target satellite, common configuration of the target satellite cell, and preset private configuration of the target satellite cell.

2. The method according to claim 1, characterized in that: The terminal receives downlink data transmitted by the satellite in real time and caches it locally.

3. The method according to claim 1, characterized in that: The carrier frequencies of the current satellite and the target satellite are different. When switching, the terminal controls the radio frequency module to switch the frequency.

4. The method according to claim 1, characterized in that: It also includes post-calibration. When the service transmission service switches from the current satellite to the target satellite, the terminal also fine-tunes the cached synchronization status information according to the downlink SSB signal of the target satellite to improve demodulation reliability.

5. The method according to claim 1, characterized in that: It also includes pre-calculation. Before switching service transmission, the terminal performs interpolation calculation based on the change in the frame boundary offset and calculates the frame boundary adjustment value that matches the current time in combination with its own real-time time to ensure that the switching time parameters are accurate.

6. The method according to claim 1, characterized in that: When the terminal detects that the signal quality of the current satellite meets the switching conditions or when the terminal receives a switching instruction from the current satellite, the terminal switches the service transmission service to the target satellite.

7. A method for switching low-Earth orbit communication satellites, the method being applied to the satellite side, characterized in that, The method includes the following steps: The current satellite receives synchronization status information sent by the target satellite via inter-satellite link; The current satellite encapsulates the synchronization status information of the target satellite into downlink data and sends it to the currently accessed terminal in real time. This enables the terminal to demodulate the downlink signal of the target satellite and send uplink services when switching satellites, using the latest received synchronization status information, so that the terminal's service transmission service can be switched from the current satellite to the target satellite. The synchronization status information includes UTC time, uplink carrier frequency of the target satellite, downlink carrier frequency of the target satellite, time offset of the target satellite, frequency offset of the target satellite, physical cell ID of the target satellite, common configuration of the target satellite cell, and preset private configuration of the target satellite cell.

8. The method according to claim 7, characterized in that: The current satellite transmits downlink data in period Y. Before the current satellite transmits downlink data, it is necessary to deduce the change in the frame boundary offset of the target satellite. The deduction time is X, where X < Y.

9. The method according to claim 7, characterized in that: Currently, the satellite also transmits its synchronization status information in real time to satellites ahead of it in its direction of travel via inter-satellite links.

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