Terminal access method, base station, terminal and non-ground communication system

Abstract

The invention provides a terminal access method, a base station, a terminal and a non-ground communication system, and the terminal access method applied to the base station comprises the steps: generating a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal comprises a space-time synchronization signal and a frequency offset measurement signal; the space-time synchronization signal carries base station direction information and timing time information of the base station; the frequency offset measurement signal carries a pilot frequency sequence; and sending a cell synchronization auxiliary signal to the terminal to enable the terminal to demodulate the cell synchronization auxiliary signal, and performing terminal access based on the demodulated base station direction information, the timing time information and the pilot frequency sequence. According to the scheme, the base station direction information and the timing time information are integrated into the space-time synchronization signal, so that the terminal can complete direction alignment and symbol timing without acquiring dynamic parameters of the base station in advance, and the initial access success rate of the terminal can be improved.

Description

Technical Field

[0001] The present application relates to the field of wireless communication technology, and in particular to a terminal access method, a base station, a terminal, and a non-terrestrial communication system. Background Art

[0002] In non-terrestrial 5G wireless communication systems, initial terminal access relies on detecting cell synchronization signals. Base stations (such as low-orbit satellites) periodically transmit synchronization signals according to the protocol's pre-defined time-frequency resources and beam directions. Terminals must continuously receive signals at a known or estimated receiving direction and frequency, and compensate for Doppler shifts caused by the base station's high-speed motion before completing synchronization detection and entering the subsequent access process. To achieve this, terminals typically rely on external information such as ephemeris and GPS / Beidou to pre-calculate the satellite's position, motion, and signal arrival direction, thereby capturing the synchronization signal at the correct time, frequency, and spatial beam.

[0003] However, the aforementioned terminal access methods rely heavily on the real-time and accuracy of base station dynamic information (including base station motion direction and status). When a terminal is disconnected from the network for an extended period or in an area without ground network coverage, ephemeris failure prevents accurate calculation of the receive beam direction, forcing the terminal to resort to compromise solutions such as beam scanning or wide-beam reception. However, beam scanning carries the risk of search failure, while wide-beam reception weakens signal strength due to reduced array gain. Both methods achieve access in scenarios without dynamic base station node information at the expense of a certain access success rate. Consequently, the aforementioned terminal access methods have a low access success rate. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a terminal access method, a base station, a terminal and a non-terrestrial communication system to solve the above-mentioned problems.

[0005] In the first aspect, an embodiment of the present application provides a terminal access method, which is applied to a base station, the method comprising: generating a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal comprises a space-time synchronization signal and a frequency offset measurement signal; the space-time synchronization signal carries the base station direction information and timing information of the base station; the frequency offset measurement signal carries a pilot sequence; and sending the cell synchronization auxiliary signal to the terminal so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, the timing information, and the pilot sequence. In the implementation process of the above scheme, by integrating the base station direction information and the timing information into the space-time synchronization signal, the terminal can complete the direction alignment and symbol timing without obtaining the base station dynamic parameters in advance, which is conducive to improving the initial access success rate of the terminal; on the other hand, the frequency offset measurement signal is sent in the form of a fixed pilot sequence. After obtaining the direction and timing information, the terminal can directly use the sequence to estimate and compensate for the residual frequency offset, avoiding secondary signaling interaction and reducing the air interface load; on the other hand, the base station direction information, timing information, and pilot sequence are all transmitted in a signal embedded manner, and the terminal can complete the terminal access process without external assistance, thereby improving the reliability of terminal access.

[0006] In an implementation of the first aspect, the space-time synchronization signal includes a main space-time synchronization signal and a secondary space-time synchronization signal; the method for determining the space-time synchronization signal includes: obtaining a main space-time synchronization signal sequence and a secondary space-time synchronization signal sequence; in the baseband frequency domain, mapping the main space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and performing modulation processing to obtain the main space-time synchronization signal; in the baseband frequency domain, mapping the secondary space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and performing modulation processing to obtain the secondary space-time synchronization signal. In the implementation process of the above scheme, by mapping the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence to the central subcarrier position of the first bandwidth of the preset beam, unified resource allocation is achieved under the same center frequency, the RF front-end filtering and carrier configuration are simplified, and the hardware complexity is reduced; on the other hand, the center subcarrier mapping can reduce the filtering roll-off and adjacent channel interference that may be introduced by the edge frequency band, so that the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence obtain symmetrical and consistent channel responses in the frequency domain, thereby improving the detection reliability of the cell synchronization auxiliary signal; on the other hand, the design of the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence being sequentially cascaded in the time domain and co-centered in the frequency domain can enable the terminal to continuously capture the auxiliary space-time synchronization signal without re-tuning the local oscillator after completing the coarse timing, which is conducive to shortening the terminal access time.

[0007] In an implementation of the first aspect, the base station direction information of the base station includes spatial wave positions; after obtaining the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence, the method further includes: obtaining the first index of the main space-time synchronization signal sequence and the second index of the auxiliary space-time synchronization signal sequence; based on the first index and the second index, obtaining the index group of the synchronization signal sequence group composed of the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence; assigning a spatial wave position uniquely corresponding to each index group; wherein the spatial wave position is used to indicate the spatial pointing of the base station relative to the terminal. During the implementation of the above scheme, a unique index group consisting of the first index of the primary synchronization signal sequence and the second index of the secondary synchronization signal sequence is mapped to a unique spatial wave position, so that the terminal can directly obtain the spatial pointing of the base station relative to the terminal after completing the synchronization detection, without the need for additional direction-finding hardware or signaling interaction, thereby reducing the implementation complexity; on the other hand, the spatial wave position discretizes the entire hemisphere coverage area in the form of solid angle units, and the index group corresponds one-to-one to the spatial wave position, which is conducive to improving the direction indication accuracy and mapping uniqueness, and avoiding beam alignment errors caused by multi-wave position ambiguity; on the other hand, the mapping relationship can be solidified before the system is deployed, and the terminal side only needs to look up the table to parse the direction information, which is conducive to reducing air interface overhead and shortening the initial access delay; on the other hand, the mapping mechanism of the index group and the spatial wave position reuses the existing synchronization sequence resources, without the need to add a new direction signaling field, thereby improving spectrum efficiency and maintaining compatibility with the current frame structure specification.

[0008] In an implementation of the first aspect, the method also includes: determining the first subcarrier spacing of the main space-time synchronization signal based on the system downlink subcarrier spacing; wherein the system downlink subcarrier spacing is determined by the system frame structure; the first subcarrier spacing is smaller than the system downlink subcarrier spacing, and the first subcarrier spacing is larger than the intra-beam frequency offset protection interval; the intra-beam frequency offset protection interval is used to characterize the minimum frequency domain protection interval required by the terminal within the coverage range of the same beam, and the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency offset between the downlink beam center and the downlink beam edge position. In the implementation process of the above scheme, by setting the first subcarrier spacing of the main space-time synchronization signal to a value smaller than the system downlink subcarrier spacing and larger than the intra-beam frequency offset protection interval, it helps to extend the symbol duration and improve the signal energy concentration, thereby improving the detection probability of the main space-time synchronization signal under wide beam reception conditions and enhancing the robustness of initial access; on the other hand, the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency offset between the downlink beam center and the beam edge, so that the first subcarrier spacing can cover the maximum residual frequency offset at any terminal position, which helps to ensure that the main space-time synchronization signal is complete and distortion-free in the frequency domain, and reduces the risk of synchronization failure caused by frequency offset; on the other hand, the narrowband design of the first subcarrier spacing reduces the occupation of spectrum resources while maintaining frequency offset tolerance, reserving more idle bandwidth for the frequency offset measurement signal in the cell synchronization auxiliary signal, and optimizing the resource allocation efficiency of the entire cell synchronization auxiliary signal.

[0009] In an implementation of the first aspect, the method further includes: determining a second subcarrier spacing of the auxiliary space-time synchronization signal based on the system downlink subcarrier spacing; wherein the system downlink subcarrier spacing is determined by the system frame structure; and the second subcarrier spacing is equal to the system downlink subcarrier spacing. In the implementation process of the above scheme, by setting the second subcarrier spacing of the auxiliary space-time synchronization signal to be equal to the system downlink subcarrier spacing, the auxiliary space-time synchronization signal is kept consistent with the subsequent broadcast channel in terms of frequency domain position, symbol duration and cyclic prefix length, so that after completing the capture of the main space-time synchronization signal, the terminal can directly parse the auxiliary space-time synchronization signal without reconfiguring the baseband parameters, thereby reducing the state switching delay; on the other hand, the auxiliary space-time synchronization signal is synchronously aligned with the system resource grid, reducing the frequency domain resampling or interpolation operation caused by the difference in subcarrier spacing, and reducing the digital front-end calculation amount and power consumption overhead; on the other hand, the unified subcarrier spacing enables all terminals in the beam to use the same frequency offset compensation coefficient at any position, and the network side does not need to send additional calibration information for different terminal positions, thereby simplifying the system signaling process.

[0010] In an implementation of the first aspect, the method further includes: determining the first bandwidth of the space-time synchronization signal; wherein the first bandwidth is not less than the minimum frequency domain protection bandwidth; the minimum frequency domain protection bandwidth is determined based on the occupied bandwidth of the space-time synchronization signal and the full-link frequency offset protection bandwidth; the full-link frequency offset protection bandwidth is determined based on the system's maximum downlink Doppler frequency offset. In the implementation of the above scheme, the lower limit of the first bandwidth is set to be no less than the minimum frequency domain protection bandwidth, which can ensure that the space-time synchronization signal always has sufficient frequency domain resources within the entire beam coverage range, avoid spectrum truncation, and improve the terminal detection success rate; on the other hand, the minimum frequency domain protection bandwidth is jointly determined by the occupied bandwidth and the full-link frequency offset protection bandwidth, so that the resource allocation amount is accurately matched with the link Doppler condition, reducing redundant frequency bands and improving spectrum utilization; on the other hand, the full-link frequency offset protection bandwidth is calculated based on the system's maximum downlink Doppler frequency offset, which helps to simplify the network-side parameter configuration process.

[0011] In one implementation of the first aspect, before the cell synchronization auxiliary signal is sent to the terminal, the method further includes: determining the Doppler frequency deviation of the space-time synchronization signal based on the expected center frequency of the space-time synchronization signal, the base station position, the base station motion state, and the downlink beam direction; and pre-compensating the auxiliary space-time synchronization signal based on the Doppler frequency deviation. In the implementation process of the above scheme, the auxiliary space-time synchronization signal is pre-compensated for the frequency deviation before transmission based on the real-time position, motion state, and beam pointing of the base station, so that the residual frequency deviation of the downlink signal when it reaches the terminal is within a correctable range, and the terminal can directly complete the synchronization sequence detection, shortening the initial capture time; on the other hand, the frequency deviation pre-compensation only acts on the auxiliary synchronization signal, retaining the original frequency deviation tolerance of the main synchronization signal, forming a main and auxiliary hierarchical processing architecture, and taking into account both capture stability and direction resolution accuracy.

[0012] In one implementation of the first aspect, the method for determining the frequency offset measurement signal includes: determining the sequence length of the pilot sequence based on the third subcarrier spacing of the frequency offset measurement signal and the second bandwidth of the frequency offset measurement signal; generating the pilot sequence based on the sequence length; sparsely sampling the pilot sequence to obtain the pilot sequence that is sparse in the frequency domain; in the baseband frequency domain, mapping the pilot sequence to the center subcarrier position of the second bandwidth of the preset beam, and performing modulation processing to obtain the frequency offset measurement signal. In the implementation process of the above scheme, the pilot sequence length is calculated based on the third subcarrier spacing and the second bandwidth as constraints to ensure that the sequence length is strictly matched with the fixed bandwidth, thereby avoiding spectrum waste and simplifying resource planning; on the other hand, after sparse sampling of the pilot sequence in the baseband frequency domain, it is mapped to the center subcarrier to form a pilot sequence, so that the terminal can still accurately extract phase information within a wide frequency offset range, thereby improving the frequency offset estimation accuracy; on the other hand, sparse sampling reduces the pilot density while maintaining the estimation performance, reduces the pilot overhead, and improves spectrum utilization.

[0013] In an implementation of the first aspect, the method further includes: determining the third subcarrier spacing of the frequency domain measurement signal; wherein the third subcarrier spacing is greater than the full-link frequency offset protection bandwidth; wherein the full-link frequency offset protection bandwidth is determined based on the system downlink maximum Doppler frequency offset. In the implementation of the above scheme, by setting the third subcarrier spacing to be greater than the full-link frequency offset protection bandwidth, the frequency offset measurement signal remains resolvable within the full-link frequency offset range, and the terminal can directly extract the frequency offset estimation result; on the other hand, a larger spacing can reduce the pilot density, reduce resource overhead, and improve spectrum utilization.

[0014] In an implementation of the first aspect, the preset beam is an access beam; wherein the access beam is a downlink beam used for initial access in the base station; the sending of a cell synchronization auxiliary signal to the terminal includes: using idle bandwidth resources in the access beam to send a cell synchronization auxiliary signal to the terminal; wherein the sum of the first bandwidth of the space-time synchronization signal and the second bandwidth of the frequency deviation measurement signal is not greater than the idle bandwidth resources. During the implementation of the above solution, the idle bandwidth of the access beam is used to transmit the cell synchronization auxiliary signal, eliminating the need to set up separate frequency domain resources for the cell synchronization auxiliary signal, which helps improve spectrum utilization and reduce the complexity of system bandwidth planning. On the other hand, the sum of the first bandwidth and the second bandwidth is limited by the idle bandwidth to avoid interference with other channels. On the other hand, the transmission parameters of the access beam have been optimized for the initial capture scenario to ensure reliable reception by the terminal without prior information. The cell synchronization auxiliary signal reuses these parameters and shares the same gain, coverage and power control link with existing service signals, eliminating the need for an independent beam management module, thereby simplifying the onboard RF link design. On the other hand, the fixed mapping mechanism of the idle bandwidth of the access beam allows the base station to send the cell access signal and cell synchronization auxiliary signal to the terminal through the access beam with only one configuration, avoiding the signaling overhead caused by dynamic resource scheduling and helping to simplify the onboard processing process.

[0015] In one implementation of the first aspect, the sending of a cell synchronization auxiliary signal to a terminal includes: continuously sending a space-time synchronization signal to the terminal; and continuously or periodically sending a frequency deviation measurement signal to the terminal. During the implementation of the above solution, the continuous transmission of the space-time synchronization signal allows the terminal to capture the synchronization signal throughout the entire access window, avoiding missed detection due to intermittent transmission, improving the probability of first capture, and shortening the search time. Furthermore, the frequency deviation measurement signal is continuously or periodically transmitted in the same beam as the space-time synchronization signal. After obtaining coarse synchronization, the terminal can perform frequency deviation estimation without waiting for additional triggering, thereby reducing access latency.

[0016] In the second aspect, an embodiment of the present application provides a terminal access method, which is applied to a terminal, and the method includes: receiving a space-time synchronization signal in a cell auxiliary synchronization signal sent by a base station; determining the base station direction information and timing time information of the base station based on the space-time synchronization signal; after obtaining the base station direction information and the timing time information, receiving a frequency deviation measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency deviation measurement signal carries a pilot sequence; performing residual frequency deviation compensation on a subsequently received downlink signal based on the pilot sequence; and after detecting a cell access signal, completing terminal access based on the cell access signal.

[0017] In a third aspect, an embodiment of the present application provides a terminal access method, the method comprising: a base station executing the following steps: generating a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a space-time synchronization signal and a frequency deviation measurement signal; the space-time synchronization signal carries the base station direction information and timing time information of the base station; the frequency deviation measurement signal carries a pilot sequence; sending a cell synchronization auxiliary signal to the terminal so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, the timing time information and the pilot sequence; the terminal executing the following steps: receiving the space-time synchronization signal in the cell auxiliary synchronization signal sent by the base station; determining the base station direction information and the timing time information of the base station based on the space-time synchronization signal; after obtaining the base station direction information and the timing time information, receiving the frequency deviation measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency deviation measurement signal carries the pilot sequence; performing residual frequency deviation compensation on the subsequently received downlink signal based on the pilot sequence; after detecting the cell access signal, completing terminal access based on the cell access signal.

[0018] In the fourth aspect, an embodiment of the present application provides a base station, including: a cell synchronization auxiliary signal generation module, used to generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a space-time synchronization signal and a frequency deviation measurement signal; the space-time synchronization signal carries the base station direction information and timing time information of the base station; the frequency deviation measurement signal carries a pilot sequence; a cell synchronization auxiliary signal sending module, used to send a cell synchronization auxiliary signal to a terminal, so that the terminal demodulates the cell synchronization auxiliary signal, and performs terminal access based on the demodulated base station direction information, the timing time information and the pilot sequence.

[0019] In the fifth aspect, an embodiment of the present application provides a terminal, including: a space-time synchronization signal receiving module, used to receive the space-time synchronization signal in the cell auxiliary synchronization signal sent by the base station; a space-time synchronization signal demodulation module, used to determine the base station direction information and timing time information of the base station based on the space-time synchronization signal; a frequency deviation measurement signal receiving module, used to receive the frequency deviation measurement signal in the cell auxiliary synchronization signal sent by the base station after obtaining the base station direction information and the timing time information; wherein, the frequency deviation measurement signal carries a pilot sequence; a residual frequency deviation compensation module, used to perform residual frequency deviation compensation on the subsequently received downlink signal based on the pilot sequence; a terminal access module, used to complete terminal access based on the cell access signal after detecting the cell access signal.

[0020] In the sixth aspect, an embodiment of the present application provides a non-terrestrial communication system, comprising a base station provided by the fourth aspect or any possible implementation of the fourth aspect and a terminal provided by the fifth aspect or any possible implementation of the fifth aspect, wherein the terminal is communicatively connected to the base station.

[0021] In the seventh aspect, an embodiment of the present application provides an electronic device, comprising: a processor, a memory and a communication bus, wherein the processor and the memory communicate with each other through the communication bus; the memory stores computer program instructions that can be executed by the processor, and when the computer program instructions are read and run by the processor, the method provided by the first aspect or any possible implementation of the first aspect is executed.

[0022] In an eighth aspect, an embodiment of the present application provides a computer-readable storage medium, on which computer program instructions are stored. When the computer program instructions are read and run by a processor, the method provided by the first aspect or any possible implementation of the first aspect or the second aspect or any possible implementation of the second aspect is executed.

[0023] In the ninth aspect, an embodiment of the present application provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, it implements the method provided by the first aspect or any possible implementation of the first aspect or the second aspect or any possible implementation of the second aspect.

[0024] Other features and advantages of the present application will be described in the following description and, in part, will become apparent from the description or be understood by practicing the embodiments of the present application. The objectives and other advantages of the present application can be achieved and obtained through the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 A schematic diagram of a multi-beam mobile satellite communication system provided in an embodiment of the present application; Figure 2 A schematic diagram of a flow chart of a terminal access method applied to a base station provided in an embodiment of the present application; Figure 3A schematic diagram of a process flow of a terminal access method applied to a terminal provided in an embodiment of the present application; Figure 4 A flowchart of a terminal access method provided in an embodiment of the present application; Figure 5 A schematic diagram of the structure of a base station provided in an embodiment of the present application; Figure 6 A schematic diagram of the structure of a terminal provided in an embodiment of the present application; Figure 7 A schematic diagram of the structure of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The following will describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application and are therefore only examples and cannot be used to limit the scope of protection of the present application.

[0028] Initial terminal access refers to the process in which the terminal attempts to establish a wireless connection with a base station for the first time. This process is the prerequisite for the terminal to enter the network and obtain communication services. The process of initial terminal access mainly includes: (1) Obtaining ephemeris information: The terminal obtains the satellite's ephemeris information (including the satellite's position, speed, orbit parameters, etc.) through built-in storage or external networks (such as ground stations, cellular networks). This information has a certain timeliness and needs to be updated regularly. (2) Calculating satellite dynamic information: The terminal combines its own real-time position (real-time position can be obtained through positioning systems such as GPS and Beidou) and uses ephemeris information to calculate the satellite's real-time position, movement direction, speed and other dynamic information at the current moment. (3) Calculating the receiving beam direction: Based on the relative geometric relationship between the terminal's own position and the satellite's real-time position, the azimuth and elevation angle of the satellite relative to the terminal are calculated, thereby determining the receiving beam direction required for the terminal to receive satellite signals. (4) Calculating the Doppler frequency deviation value: Based on the radial velocity of the satellite relative to the terminal, the downlink Doppler frequency deviation value (frequency offset) caused by high-speed movement is calculated. (5) Configure receiving parameters: Based on the calculation results, the terminal adjusts its receiving beam to point in the direction of the satellite and continuously receives the cell synchronization signal transmitted by the satellite on the fixed frequency resources pre-defined by the communication protocol. (6) Doppler offset compensation: The terminal performs Doppler offset compensation on the received signal to eliminate the signal distortion caused by frequency offset. (7) Detect cell access signal: After completing the above steps, the terminal can accurately detect and demodulate the cell access signal transmitted by the satellite, successfully completing the initial access process.

[0029] Before initiating the access process, the terminal needs to obtain the base station's direction and motion status information (the base station's direction and motion status information can be collectively referred to as the base station's dynamic information) to calculate the appropriate signal reception beam direction. For example, in satellite communication systems, the terminal generally uses ephemeris to obtain this information. Ephemeris is input from the ground network or obtained from base station information after the terminal last accessed the satellite network. Ephemeris information has a certain timeliness. If it is not updated for a long time, it will produce large errors or even become unusable. Therefore, in some application scenarios, such as in areas without other communication network coverage and scenarios where the terminal has not accessed the satellite network for a long time, the terminal cannot pre-calculate the appropriate signal reception beam direction, making it difficult for the terminal to complete the initial access process.

[0030] Currently, there are roughly three types of solutions for addressing these scenarios. The first type involves beam scanning. When a terminal lacks prior information about the base station's current location or beam direction, it can continuously switch its receiving beam direction according to a predetermined pattern (such as a random or fixed sequence) to search for the cell synchronization signal within all possible spatial angles. However, the base station's cell synchronization signal is not always transmitted omnidirectionally. Instead, it is transmitted intermittently, along its own high-speed trajectory, in a direction that changes over time. Therefore, the terminal's scanning beam and the base station's transmit beam must coincide in time and space to detect the signal. If they are misaligned, even if the terminal scans all directions, it may still fail to capture the synchronization signal, resulting in failed access or extremely time-consuming access. The second type involves wide-beam reception. The terminal uses a wide-beam receiving beam to cover potential airspace in order to capture the cell synchronization signal transmitted by the satellite base station. This solution expands beam coverage in exchange for a simplified spatial search dimension, thus avoiding reliance on real-time satellite position information. However, beamwidth is inversely proportional to antenna array gain. According to antenna theory, beam widening leads to a decrease in effective array gain, and thus a decrease in received signal power. Under conditions of limited satellite link budgets, the signal-to-noise ratio (SCR) will also deteriorate, reducing the probability of synchronization sequence detection. When the signal strength falls below the receiver sensitivity threshold, the terminal will be unable to complete downlink synchronization, ultimately leading to access failure. The third type of solution: combining beam scanning solutions with wide-beam reception solutions. In summary, existing technologies achieve access capabilities in scenarios without dynamic base station node information at the expense of a certain probability of successful access, which may result in excessively long access times or even inability to access the network.

[0031] In view of this, an embodiment of the present application provides a terminal access method, which integrates the base station direction information and timing time information into the space-time synchronization signal. The terminal can complete direction alignment and symbol timing without pre-acquiring the base station dynamic parameters, which is beneficial to improving the initial access success rate of the terminal; on the other hand, the frequency deviation measurement signal is sent in the form of a fixed pilot sequence. After obtaining the direction and timing information, the terminal can directly use the sequence to estimate and compensate for the residual frequency deviation, avoid secondary signaling interaction, and reduce the air interface load; on the other hand, the base station direction information, timing information and pilot sequence are all transmitted in a signal embedded manner, and the terminal can complete the terminal access process without external assistance, thereby improving the reliability of terminal access.

[0032] Before introducing the above-mentioned terminal access method, its application scenario is introduced first: the technical solution of the present application can be applied to non-terrestrial network (NTN) systems such as satellite communication systems and high altitude platform station (HAPS) communications, for example, integrated communication and navigation (ICaN) systems, global navigation satellite systems (GNSS), etc. Satellite communication systems can be integrated with traditional mobile communication systems. For example, mobile communication systems can be fourth-generation (4G) communication systems (such as Long Term Evolution (LTE) systems), Worldwide interoperability for Microwave Access (WiMAX) communication systems, fifth-generation (5G) communication systems (such as New Radio (NR) systems), and future mobile communication systems. Please refer to Figure 1 , Figure 1 Schematic diagram of a multi-beam mobile satellite communication system applicable to an embodiment of the present application. Figure 1As shown, a satellite provides communication services to terminal devices using multiple beams. The satellite in this scenario is a non-geostationary Earth orbit (NGEO) satellite, connected to core network equipment. The satellite uses multiple beams to cover its service area, and different beams can communicate using one or more of time division, frequency division, and space division. The satellite provides communication and navigation services to terminal devices by broadcasting communication signals and navigation signals. The satellites mentioned in the embodiments of this application may also be satellite base stations or network-side devices carried on satellites. For example, satellite communication systems can be divided into the following three types based on the satellite's orbital altitude: geostationary Earth orbit (GEO) satellite communication systems, also known as synchronous orbit satellite communication systems; medium Earth orbit (MEO) satellite communication systems; and low Earth orbit (LEO) satellite communication systems. GEO satellites have an orbital altitude of 35,786 km. Their main advantage is that they can remain stationary relative to the ground and provide a large coverage area. However, GEO satellite communications also have significant drawbacks: GEO satellite orbits are far from Earth, resulting in high free-space propagation losses, which constrain communication link budgets. Furthermore, to increase transmit and receive gain, satellites require larger antennas. GEO communication transmission latency is high, reaching around 500ms round-trip, making it inadequate for low-latency services. GEO orbital resources are also relatively limited, resulting in high launch costs and a lack of coverage of the polar regions. MEO satellites, with orbital altitudes between 2000 and 35786 km, offer the advantage of enabling global coverage with a relatively small number of satellites. However, their orbital altitudes are higher than those of LEO satellites, and transmission latency is still higher than that of LEO satellites. LEO satellites, with orbital altitudes between 300 and 2000 km, offer advantages such as lower data transmission latency, reduced transmission losses, and lower launch costs. Of course, in certain application scenarios, LEO satellites can be replaced with GEO or MEO satellites, or even a combination of these types of satellites.

[0033] The following will describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings. Figure 2 , an embodiment of the present application provides a terminal access method, the method comprising: Step S110: Generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency offset measurement signal; the time-space synchronization signal carries the base station direction information and timing information of the base station; the frequency offset measurement signal carries a pilot sequence.

[0034] The space-time synchronization signal in the cell synchronization auxiliary signal is used to convey the spatial orientation and symbol timing reference of the satellite base station to the terminal in the downlink, enabling the terminal to complete beam alignment and symbol boundary alignment without knowing the base station's dynamic information. The frequency offset measurement signal provides the terminal with a known pilot sequence in the downlink, enabling the terminal to estimate and compensate for residual Doppler offset through phase or frequency domain processing, ensuring the accuracy of subsequent data demodulation. The base station direction information refers to the azimuth-elevation vector with the ground terminal as the reference origin, indicating the spatial orientation of the satellite base station relative to the terminal, allowing the terminal to adjust the receive beam direction. Timing information refers to the downlink symbol start time and radio frame boundary, which is used by the terminal to align the OFDM (Orthogonal Frequency Division Multiplexing) demodulation window to avoid inter-symbol interference. The pilot sequence is a predefined, complex-valued sequence known to the terminal. It is embedded in the frequency offset measurement signal, and its phase rotation is used by the terminal to calculate and correct the Doppler offset in the downlink. It is understandable that the cell access signal is mentioned in the introduction to the initial access process of the terminal in the above content. The following describes the difference between the cell access signal and the cell synchronization auxiliary signal in the solution provided in the embodiment of the present application: the cell access signal refers to a set of downlink physical layer signals specially transmitted by the satellite base station for the initial access of the terminal to the network, which may include the primary synchronization sequence (PSS), the secondary synchronization sequence (SSS), the physical broadcast channel (PBCH) and the master information block (MIB) it carries. The cell access signal generally adopts service-level subcarrier spacing and dynamic scheduling resources. Its transmission period, bandwidth and beam pointing vary with service requirements, and cannot meet the terminal's demand for continuous, fixed, narrowband synchronization resources in scenarios without prior information. The newly added cell synchronization auxiliary signal can carry direction information, timing reference and pilot sequence, thereby realizing an independent link for the terminal's first capture, frequency offset estimation and direction alignment without interfering with existing services, ensuring the initial access success rate and delay indicators. In addition, the process in which the terminal uses the above-mentioned cell synchronization auxiliary signal to complete direction capture, timing synchronization and frequency offset estimation can be called a blind access process. After the process is completed, the terminal still needs to receive and parse the cell access signal to obtain the random access configuration, and then execute the random access process to complete the final terminal access.

[0035] The following describes the composition and generation scheme of the above-mentioned cell synchronization auxiliary signal: Optionally, the above-mentioned space-time synchronization signal includes a primary space-time synchronization signal and a secondary space-time synchronization signal. The method for determining the space-time synchronization signal in the above-mentioned cell synchronization auxiliary signal includes: obtaining a primary space-time synchronization signal sequence and a secondary space-time synchronization signal sequence; in the baseband frequency domain, mapping the primary space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and performing modulation processing to obtain the primary space-time synchronization signal; in the baseband frequency domain, mapping the secondary space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and performing modulation processing to obtain the secondary space-time synchronization signal. The above-mentioned primary space-time synchronization signal sequence and secondary space-time synchronization signal sequence are both discrete complex-valued sequences generated by the base station, and can respectively adopt the PSS (Primary Synchronization Signal) root sequence and SSS (Secondary Synchronization Signal) root sequence defined in the 5G NR specification, and both have a length of 127 symbols. The primary space-time synchronization signal sequence is mainly used by the terminal to extract the symbol timing reference and expand the frequency deviation tolerance. The secondary space-time synchronization signal sequence is used by the terminal to obtain the direction index of the satellite base station and confirm the frame boundary. The two can be mapped to the same bandwidth center subcarrier in the baseband frequency domain and then modulated to obtain the corresponding time domain synchronization signal.

[0036] The above scheme forms a single carrier reference in the frequency domain by mapping the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence to the same bandwidth position of the preset beam, so that the base station can carry the two synchronization sequences simultaneously with only one RF configuration, avoiding the additional local oscillator and filtering resources required for the separate center frequencies. The shared center subcarrier can also enable the two sequences to experience the same channel response, eliminating the gain mismatch caused by the difference in frequency domain position. After capturing the main space-time synchronization signal sequence, the terminal can seamlessly receive the auxiliary space-time synchronization signal sequence at the same frequency point without re-tuning, shortening the synchronization time and reducing the hardware complexity. In addition, after the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence are inverse Fourier transformed, they are connected end to end in the time domain in the order of main first and auxiliary later to form a continuous symbol stream, so that the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence are sequentially cascaded in the time domain and co-centered in the frequency domain.

[0037] Exemplarily, the above-mentioned scheme for modulating the synchronization signal sequence to obtain the synchronization signal can be: after completing the sequence mapping in the baseband frequency domain, performing an inverse discrete Fourier transform on the mapping result to generate a time domain OFDM symbol, and inserting a cyclic prefix at the front end of the symbol to form a synchronization signal.

[0038] The above scheme realizes unified resource allocation under the same center frequency by mapping the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence to the central subcarrier position of the first bandwidth of the preset beam, simplifies the RF front-end filtering and carrier configuration, and reduces hardware complexity; on the other hand, the center subcarrier mapping can reduce the filtering roll-off and adjacent channel interference that may be introduced by the edge frequency band, so that the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence obtain symmetrical and consistent channel responses in the frequency domain, thereby improving the detection reliability of the cell synchronization auxiliary signal; on the other hand, the design of the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence being sequentially cascaded in the time domain and co-centered in the frequency domain can enable the ground terminal to continuously capture the auxiliary space-time synchronization signal after completing the coarse timing without re-tuning the local oscillator, which is conducive to shortening the terminal access time.

[0039] The following describes how the aforementioned space-time synchronization signal carries base station direction information: Optionally, the base station direction information includes spatial wavelet information. After obtaining the primary space-time synchronization signal sequence and the secondary space-time synchronization signal sequence, the terminal access method further includes: obtaining a first index of the primary space-time synchronization signal sequence and a second index of the secondary space-time synchronization signal sequence; based on the first index and the second index, obtaining an index group of a synchronization signal sequence group consisting of the primary space-time synchronization signal sequence and the secondary space-time synchronization signal sequence; and assigning a unique spatial wavelet information to each index group; wherein the spatial wavelet information indicates the spatial orientation of the base station relative to the terminal. The principle by which the aforementioned space-time synchronization signal can carry base station direction information is as follows: assuming that the primary space-time synchronization signal sequence uses the PSS format and the secondary space-time synchronization signal sequence uses the SSS format. Therefore, the primary space-time synchronization signal sequence has a value range of 0, 1, and 2, for a total of 3 types. The secondary space-time synchronization signal sequence has a value range of 0 to 335, for a total of 336 types. By combining the primary and secondary space-time synchronization signal sequence values, 3 × 336 = 1008 unique index groups can be formed. Before assigning a unique spatial wave position to an index group, the spatial wave position can be divided. For example, with the ground terminal as the origin, the upper hemisphere airspace is discretely divided into 1008 non-overlapping solid angle units, each of which is a spatial wave position. Each spatial wave position is sequentially assigned a unique number from 0 to 1007. Finally, a one-to-one mapping table can be established between the 1008 index pairs and the 1008 spatial wave position numbers. When the terminal detects a certain index group, it can directly obtain the corresponding spatial wave position number by looking up the table, thereby determining the spatial orientation of the base station relative to the terminal.

[0040] For example, the above-mentioned method of dividing the airspace wave position is as follows: with the ground terminal as the origin, the entire upper hemisphere airspace is discretized into a finite number of non-overlapping solid angle units. First, the airspace boundary is determined based on the satellite orbit altitude and the ground visibility range to ensure coverage of all possible service elevation angles. Subsequently, the latitude and longitude grid or regular polyhedron subdivision method is used to subdivide the airspace step by step into a number of sub-regions of equal area or equal solid angle. Each sub-region corresponds to a spatial wave position and is assigned a unique index. During the division process, the angular intervals between adjacent wave positions are kept uniform to avoid beam pointing blind spots or overlaps. The final wave position set does not exceed the specified number, and the center direction of each wave position is known and fixed, which can be used as a benchmark for terminal receiving beam alignment and directional information mapping.

[0041] The above scheme maps a unique index group consisting of the first index of the primary synchronization signal sequence and the second index of the secondary synchronization signal sequence to a unique spatial wave position, so that the terminal can directly obtain the spatial pointing of the base station relative to the terminal after completing the synchronization detection, without the need for additional direction-finding hardware or signaling interaction, thereby reducing the implementation complexity; on the other hand, the spatial wave position discretizes the entire hemisphere coverage area in the form of solid angle units, and the index group corresponds one-to-one to the spatial wave position, which is conducive to improving the direction indication accuracy and mapping uniqueness, and avoiding beam alignment errors caused by multi-wave position ambiguity; on the other hand, the mapping relationship can be solidified before the system is deployed, and the terminal side only needs to look up the table to parse the direction information, which is conducive to reducing air interface overhead and shortening the initial access delay; on the other hand, the mapping mechanism of the index group and the spatial wave position reuses the existing synchronization sequence resources, without the need to add a new direction signaling field, thereby improving spectrum efficiency and maintaining compatibility with the current frame structure specification.

[0042] The frequency deviation pre-compensation scheme of the space-time synchronization signal is introduced below: Optionally, before sending the cell synchronization auxiliary signal to the terminal, the terminal access method further includes: determining the Doppler frequency deviation of the space-time synchronization signal based on the expected center frequency of the space-time synchronization signal, the base station position, the base station motion state and the downlink beam direction; and pre-compensating the auxiliary space-time synchronization signal based on the Doppler frequency deviation. This implementation example: the base station transmits the space-time synchronization signal according to the frequency deviation of the cell synchronization auxiliary signal. The expected center frequency, the base station's own position and the base station's motion state determine the downlink beam direction and calculate the Doppler frequency deviation of the time-space synchronization signal. ; Then use the frequency offset compensation value Auxiliary space-time synchronization signal Perform frequency offset pre-compensation. In the above scheme, the time-space synchronization signal is transmitted The expected center frequency, the base station's own position and the base station's motion state determine the downlink beam direction and calculate the Doppler frequency deviation of the time-space synchronization signal. The method and the method of pre-compensating the frequency deviation of the auxiliary space-time synchronization signal using Doppler frequency deviation are both relatively mature existing technologies in this field. For their specific implementation methods, please refer to the relevant technologies, and the embodiments of this application will not be repeated. It can be understood that the above scheme can only pre-compensate the frequency deviation of the auxiliary space-time synchronization signal in the space-time synchronization signal. This is because the main space-time synchronization signal adopts a narrow subcarrier spacing and already has sufficient frequency deviation tolerance. Additional compensation may introduce errors. The auxiliary space-time synchronization signal carries direction information, and frequency deviation pre-compensation can further compress the residual frequency deviation and ensure accurate direction indication.

[0043] The above scheme implements frequency offset pre-compensation for the auxiliary space-time synchronization signal based on the real-time position, motion status and beam pointing of the base station before transmission, so that the residual frequency offset of the downlink signal is within the correctable range when it reaches the terminal. The terminal can directly complete the synchronization sequence detection, shortening the initial capture time; on the other hand, the frequency offset pre-compensation can only act on the auxiliary synchronization signal, retaining the original frequency offset tolerance of the main synchronization signal, taking into account both capture stability and direction resolution accuracy.

[0044] The following is an introduction to the subcarrier spacing design scheme of the above-mentioned main space-time synchronization signal and auxiliary space-time synchronization signal: Optionally, the above-mentioned terminal access method also includes: determining the first subcarrier spacing of the main space-time synchronization signal based on the system downlink subcarrier spacing; wherein the system downlink subcarrier spacing is determined by the system frame structure; the first subcarrier spacing is smaller than the system downlink subcarrier spacing, and the first subcarrier spacing is larger than the intra-beam frequency offset protection interval; the intra-beam frequency offset protection interval is used to characterize the minimum frequency domain protection interval required by the terminal within the coverage range of the same beam, and the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency deviation between the downlink beam center and the downlink beam edge. This implementation method is, for example: the main space-time synchronization signal The first subcarrier spacing is set to , and the first subcarrier spacing satisfies: .in, is the system downlink subcarrier spacing; is a positive integer; is the frequency offset protection interval within the beam; The maximum difference in Doppler frequency deviation between the downlink beam center and the downlink beam edge, in Hertz (Hz). Refers to the fixed frequency spacing between adjacent subcarriers in the downlink OFDM waveform. This parameter is uniformly set by the system frame structure specification and directly affects the symbol duration, cyclic prefix length, and the maximum supported Doppler tolerance. It is the basic granularity of physical layer processes such as waveform generation, resource mapping, and frequency offset estimation. System downlink subcarrier spacing The value of can be selected from discrete gears such as 15kHz, 30kHz, 60kHz, 120kHz, and 240kHz. The corresponding relationship is indicated by numerology in high-level signaling. In 5G NR, numerology refers to the parameter combination of subcarrier spacing and symbol duration. The method for determining it is referred to the prior art and will not be repeated in this embodiment of the application.

[0045] In addition, since the 5G NR physical layer specification limits all subcarrier spacing to only integer powers of 15kHz multiplied by 2, the above proportional coefficient can be Set to a positive integer, so that the first subcarrier spacing can be guaranteed It remains within the aforementioned discrete set, thereby maintaining an integer multiple relationship with the existing sampling clock, FFT length, and cyclic prefix length, reducing implementation complexity and ensuring terminal compatibility.

[0046] The maximum difference in Doppler frequency deviation between the downlink beam center and the downlink beam edge is It can be defined as: within the same beam coverage area, the maximum absolute value of the difference between the downlink Doppler frequency deviations caused by satellite motion at the beam edge point and the beam center point. The method for determining can be: the base station obtains the satellite velocity vector based on the real-time ephemeris, and calculates the maximum radial velocity difference of the beam edge relative to the satellite velocity direction in combination with the beam center direction and the beam angle; after mapping the velocity difference to the downlink carrier frequency, it can be obtained.

[0047] It is understandable that the above intra-beam frequency offset protection interval can be directly taken as the maximum difference in Doppler frequency offset between the downlink beam center and the downlink beam edge. twice, that is The intra-beam frequency offset protection interval is mainly used to reserve additional bandwidth for the main space-time synchronization signal in the frequency domain to ensure that the maximum bidirectional residual frequency offset that may occur at the beam edge terminal does not cause the signal energy to fall into the adjacent subcarrier. When the residual frequency offset of a beam-edge terminal exceeds the tolerance of a single OFDM subcarrier, causing inter-symbol interference (ISI), setting the first subcarrier spacing larger than the intra-beam frequency offset protection interval ensures that the residual frequency offset at all terminal locations falls within the primary synchronization signal subcarrier bandwidth. Furthermore, a larger subcarrier spacing corresponds to a longer symbol duration and higher energy concentration, allowing terminals to obtain sufficient correlation peaks even under low-gain wide beam conditions, improving the probability of first acquisition.

[0048] The above scheme helps to extend the symbol duration and improve the signal energy concentration by setting the first subcarrier spacing of the main space-time synchronization signal to a value smaller than the system downlink subcarrier spacing and larger than the intra-beam frequency offset protection interval, thereby improving the detection probability of the main space-time synchronization signal under wide-beam reception conditions and enhancing the robustness of initial access; on the other hand, the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency offset between the downlink beam center and the beam edge, so that the first subcarrier spacing can cover the maximum residual frequency offset at any terminal position, which helps to ensure that the main space-time synchronization signal is complete and distortion-free in the frequency domain, and reduce the risk of synchronization failure caused by frequency offset; on the other hand, the narrowband design of the first subcarrier spacing reduces the occupancy of spectrum resources while maintaining frequency offset tolerance, reserving more idle bandwidth for the frequency offset measurement signal in the cell synchronization auxiliary signal, and optimizing the resource allocation efficiency of the entire cell synchronization auxiliary signal.

[0049] Optionally, the terminal access method further includes: determining the second subcarrier spacing of the auxiliary space-time synchronization signal based on the system downlink subcarrier spacing; wherein the system downlink subcarrier spacing is determined by the system frame structure; and the second subcarrier spacing is equal to the system downlink subcarrier spacing. The second subcarrier spacing is set to the same as the system downlink subcarrier spacing It is understandable that the system downlink subcarrier spacing It is a fixed granularity defined by the system frame structure, and the downlink physical channels (such as broadcast channels, control channels and data channels) are all based on this granularity for resource mapping and parameter calculation. The second subcarrier spacing of the auxiliary time-space synchronization signal is directly set to the same as the system downlink subcarrier spacing. The equal values ​​ensure that the auxiliary space-time synchronization signal is consistent with the existing downlink in frequency domain position, symbol duration, cyclic prefix length and resource unit division, without introducing a new sampling rate or transform length, thereby maintaining a unified time-frequency grid and ensuring that the terminal continuously completes synchronization, system information reception and subsequent service processing under the same numerology.

[0050] The above scheme sets the second subcarrier spacing of the auxiliary space-time synchronization signal to be equal to the system downlink subcarrier spacing, so that the auxiliary space-time synchronization signal is consistent with the subsequent broadcast channel in frequency domain position, symbol duration and cyclic prefix length, so that the terminal can directly parse the auxiliary space-time synchronization signal without reconfiguring the baseband parameters after completing the capture of the main space-time synchronization signal, thereby reducing the state switching delay; on the other hand, the auxiliary space-time synchronization signal is synchronously aligned with the system resource grid, reducing the frequency domain resampling or interpolation operations caused by the difference in subcarrier spacing, and reducing the digital front-end calculation amount and power consumption overhead; on the other hand, the unified subcarrier spacing enables all terminals in the beam to use the same frequency offset compensation coefficient at any position, and the network side does not need to send additional calibration information for different terminal positions, thereby simplifying the system signaling process.

[0051] The following describes a method for determining the bandwidth occupied by a space-time synchronization signal in a preset beam: Optionally, the terminal access method further includes: determining a first bandwidth of the space-time synchronization signal; wherein the first bandwidth is not less than the minimum frequency domain protection bandwidth; the minimum frequency domain protection bandwidth is determined based on the occupied bandwidth of the space-time synchronization signal and the full-link frequency offset protection bandwidth; the full-link frequency offset protection bandwidth is determined based on the system's maximum downlink Doppler frequency offset. This implementation, for example, requires that the first bandwidth of the space-time synchronization signal satisfy the following constraints: .in, is the system downlink subcarrier spacing; Auxiliary space-time synchronization signal sequence The length of the sequence; represents a second bandwidth of the auxiliary space-time synchronization signal; is the maximum Doppler frequency deviation of the system downlink; It is the full-link frequency offset protection bandwidth.

[0052] It can be understood that the above content introduces that the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence adopt the design of time domain cascade and frequency domain co-center, and the two share the same central carrier and have different subcarrier spacing. The main space-time synchronization signal sequence adopts a narrower subcarrier spacing, and the first bandwidth of the main space-time synchronization signal sequence is always less than or equal to the second bandwidth of the auxiliary synchronization sequence. Therefore, the second bandwidth of the auxiliary space-time synchronization signal sequence, that is, using To represent the occupied bandwidth of the space-time synchronization signal.

[0053] The maximum downlink Doppler frequency deviation of the above system It refers to the maximum frequency offset value that may occur in the downlink of a non-terrestrial wireless communication system due to the high-speed movement of the satellite-borne base station. The bandwidth of the full-link frequency deviation protection can be calculated based on the downlink carrier frequency and the maximum speed of the base station. The calculation method can be found in the relevant technology and will not be described in detail in this embodiment. This is to deal with the maximum Doppler frequency deviation of the system downlink The frequency drift that may be introduced in both positive and negative directions, and the symmetrical protection band width reserved for the synchronization signal in the frequency domain, its value is equal to is twice as much as , which is used to ensure that the residual frequency offset at any terminal location does not exceed the bandwidth range. It can be understood that the above constraints represents the constraints on the spectrum width requirements of the spatiotemporal synchronization signal, Indicates the constraint imposed by the space-time synchronization signal on the maximum bidirectional downlink participating frequency offset. Together, these two constraints constitute the minimum frequency domain width requirement for the space-time synchronization signal. If the first bandwidth of the space-time synchronization signal does not meet this constraint, the residual frequency offset at beam-edge terminals will exceed the spectrum boundary, causing sequence energy to leak to adjacent subcarriers, making it impossible for the terminal to correctly decode the directional index.

[0054] The above scheme sets the lower limit of the first bandwidth to no less than the minimum frequency domain protection bandwidth, which can ensure that the time-space synchronization signal always has sufficient frequency domain resources within the entire beam coverage range, avoid spectrum truncation, and improve the terminal detection success rate; on the other hand, the minimum frequency domain protection bandwidth is jointly determined by the occupied bandwidth and the full-link frequency offset protection bandwidth, so that the resource allocation amount is accurately matched with the link Doppler conditions, reducing redundant frequency bands and improving spectrum utilization; on the other hand, the full-link frequency offset protection bandwidth is calculated based on the system's maximum downlink Doppler frequency offset, which helps to simplify the network-side parameter configuration process.

[0055] It can be understood that the difference between the main space-time synchronization signal in the embodiment of the present application and the PSS in the protocol is reflected in the redesign of the subcarrier spacing and the extension of the frequency deviation tolerance, while the difference between the auxiliary space-time synchronization signal and the SSS in the protocol is reflected in the additional carrying of spatial wave position information through the index group mapping mechanism. Specifically: the protocol PSS in the protocol is only used for symbol timing and preliminary detection of the ID within the cell group, and the main space-time synchronization signal is given the design goal of extending the frequency deviation tolerance on this basis. For this reason, its transmitting subcarrier spacing is explicitly set to a value smaller than the system downlink subcarrier spacing and larger than the frequency deviation protection interval within the beam, so that the symbol duration is extended and the energy concentration is improved, so that it can still be reliably detected when the terminal adopts wide beam reception and there is a large frequency deviation. The subcarrier spacing of the protocol PSS is fixed to be equal to the system downlink subcarrier spacing, and no additional optimization is made for wide beam scenarios. The SSS in the protocol is used only to carry the cell group ID and intra-cell group ID. While retaining this identification function, the secondary space-time synchronization signal (SSSS) also maps to one of 1008 spatial wave positions using a unique index consisting of the first index of the primary space-time synchronization signal sequence and the second index of the secondary space-time synchronization signal sequence. This embeds the spatial pointing information of the satellite base station relative to the terminal into the sequence combination. After demodulating the secondary space-time synchronization signal, the terminal can directly obtain the direction of the base station without the need for additional direction-finding hardware or signaling interaction. The SSS protocol itself does not contain any spatial pointing information.

[0056] The following is an introduction to the generation scheme of the above-mentioned frequency deviation measurement signal: Optionally, the method for determining the frequency deviation measurement signal in the above-mentioned cell synchronization auxiliary signal includes: determining the sequence length of the pilot sequence based on the third subcarrier spacing of the frequency deviation measurement signal and the second bandwidth of the frequency deviation measurement signal; generating a pilot sequence based on the sequence length; sparsely sampling the pilot sequence to obtain a sparse pilot sequence in the frequency domain; in the baseband frequency domain, mapping the pilot sequence to the center subcarrier position of the second bandwidth of the preset beam, and performing modulation processing to obtain the frequency deviation measurement signal. This implementation method is for example: first, calculate the sequence length of the pilot sequence ,in, is the third subcarrier spacing of the frequency deviation measurement signal; is a positive integer; is the second bandwidth of the frequency deviation measurement signal; then, the method of generating a pilot sequence in the existing protocol can be used to generate a signal with a length of The pilot sequence , and in Fill after each element 0, get , then Placed in the second bandwidth Finally, the frequency deviation measurement signal in the baseband time domain is generated using the method of generating a baseband time domain signal using the protocol . The above is a positive integer that can be used to adjust the sparsity of the pilot sequence. Fill after each element After the zero, the effective subcarrier spacing of the pilot sequence is expanded to the original times, forming a sparse frequency domain structure. This sparse structure helps the terminal to accurately estimate the frequency offset within a larger frequency offset range, while reducing the occupation of spectrum resources by the pilot sequence. In addition, the second bandwidth of the above-mentioned frequency offset measurement signal can be determined by the bandwidth resources that can be provided by the preset beam and the first bandwidth of the space-time synchronization signal. The occupied bandwidth of the space-time synchronization signal and the frequency offset measurement signal can be less than the bandwidth resources that can be provided by the preset beam, that is, the sum of the first bandwidth and the second bandwidth is less than the bandwidth resources that can be provided by the preset beam.

[0057] The above scheme calculates the pilot sequence length based on the third subcarrier spacing and the second bandwidth as constraints, ensuring that the sequence length strictly matches the fixed bandwidth, avoiding spectrum waste and simplifying resource planning. On the other hand, the pilot sequence is sparsely sampled in the baseband frequency domain and then mapped to the center subcarrier to form a pilot sequence, so that the terminal can still accurately extract phase information within a wide frequency offset range, thereby improving the frequency offset estimation accuracy. On the other hand, sparse sampling reduces the pilot density while maintaining estimation performance, reduces pilot overhead, and improves spectrum utilization.

[0058] The following is an introduction to the subcarrier spacing design scheme of the above-mentioned frequency deviation measurement signal: Optionally, the above-mentioned terminal access method further includes: determining the third subcarrier spacing of the frequency domain measurement signal; wherein the third subcarrier spacing is greater than the full-link frequency deviation protection bandwidth; wherein the full-link frequency deviation protection bandwidth is determined based on the system downlink maximum Doppler frequency deviation. This implementation method is, for example: setting the third subcarrier spacing of the frequency deviation measurement signal to , and satisfy: ,in, is the full-link frequency deviation protection bandwidth, is a positive integer. The third subcarrier spacing mentioned above must satisfy , is to ensure that the frequency offset measurement signal covers the maximum frequency offset range of the entire link, thereby providing accurate frequency offset estimation. This not only prevents spectrum leakage to adjacent subcarriers caused by excessive frequency offset, improving frequency offset estimation accuracy, but also enhances the robustness of the terminal access method described above under harsh conditions such as high-speed mobility, improving communication reliability and stability.

[0059] The above scheme sets the third subcarrier interval to be larger than the full-link frequency offset protection bandwidth, so that the frequency offset measurement signal remains resolvable within the full-link frequency offset range, and the terminal can directly extract the frequency offset estimation result; on the other hand, a larger interval can reduce the pilot density, reduce resource overhead, and improve spectrum utilization.

[0060] Step S120: sending a cell synchronization auxiliary signal to the terminal, so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, timing time information and pilot sequence.

[0061] Optionally, the preset beam is an access beam; wherein the access beam is a downlink beam used for initial access in the base station. Step S120 may include: utilizing idle bandwidth resources in the access beam to send a cell synchronization auxiliary signal to the terminal; wherein the sum of a first bandwidth of the space-time synchronization signal and a second bandwidth of the frequency offset measurement signal is no greater than the idle bandwidth resources.

[0062] The above-mentioned idle bandwidth resources refer to bandwidth resources that will not be occupied at all times when the access beam belongs to it. This means that during the entire operation period of the access beam, no matter how the service data or control signaling is dynamically scheduled, this part of the bandwidth can always be reserved for the cell synchronization auxiliary signal. The idle bandwidth resources can be used exclusively to carry the time-space synchronization signal and the frequency offset measurement signal, ensuring that these signals can be stably transmitted at any time without interference from other services or control signals. The above-mentioned cell synchronization auxiliary signal can be compatible with the existing cell access signal in the following three aspects: (1) Frequency domain compatibility: The cell synchronization auxiliary signal is mapped to the idle bandwidth of the access beam, and the sum of its first bandwidth and second bandwidth does not exceed the idle bandwidth resource, ensuring that there is no frequency domain overlap with the existing cell access signal to avoid interference. (2) Time domain compatibility: The cell synchronization auxiliary signal is continuously transmitted, while the existing cell access signal is dynamically scheduled on demand. The two are independent of each other in the time domain, share the same beam but do not interfere with each other. (3) Functional compatibility: The cell synchronization auxiliary signal provides the terminal with the direction, timing and pilot sequence required for initial access, and the existing cell access signal carries system information and access configuration. The two complement each other and jointly complete the terminal's network access process.

[0063] The above scheme uses the idle bandwidth of the access beam to transmit the cell synchronization auxiliary signal, and there is no need to set frequency domain resources separately for the cell synchronization auxiliary signal, which helps to improve spectrum utilization and reduce the complexity of system bandwidth planning; on the other hand, the sum of the first bandwidth and the second bandwidth is limited by the idle bandwidth to avoid interference with other channels; on the other hand, the transmission parameters of the access beam have been optimized for the initial capture scenario to ensure that the terminal can reliably receive it without prior information. The cell synchronization auxiliary signal reuses these parameters and shares the same gain, coverage and power control link with the existing service signal, without the need for an independent beam management module, thereby simplifying the onboard RF link design; on the other hand, the fixed mapping mechanism of the idle bandwidth of the access beam allows the base station to send the cell access signal and the cell synchronization auxiliary signal to the terminal through the access beam with only one configuration, avoiding the signaling overhead caused by dynamic resource scheduling, and helping to simplify the onboard processing process.

[0064] Optionally, step S120 may include: continuously transmitting a space-time synchronization signal to the terminal; and continuously or periodically transmitting a frequency offset measurement signal to the terminal. It is understood that since the space-time synchronization signal is responsible for providing the terminal with the symbol timing and base station direction information required for initial access, it is necessary to ensure that the terminal can complete synchronization capture at any time. Therefore, the space-time synchronization signal can be continuously transmitted to the terminal. The frequency offset measurement signal is used for subsequent frequency offset estimation and compensation. Therefore, the transmission mechanism of the frequency offset measurement signal can be flexibly switched between continuous and periodic transmission.

[0065] The above scheme continuously transmits the time-space synchronization signal, allowing the terminal to capture the synchronization signal within the entire access window, avoiding missed detection due to intermittent transmission, improving the probability of first capture and shortening the search time; on the other hand, the frequency deviation measurement signal is transmitted in the same beam as the time-space synchronization signal in a continuous or periodic manner. After obtaining coarse synchronization, the terminal can perform frequency deviation estimation without waiting for additional triggers, thereby reducing access delay.

[0066] See Figure 3 Based on the same inventive concept, an embodiment of the present application further provides a terminal access method applied to a terminal, the method comprising: Step S210: Receive the time and space synchronization signal in the cell auxiliary synchronization signal sent by the base station.

[0067] Within the preset first bandwidth, the terminal uses a wide beam to monitor the space-time synchronization signal from the base station. The space-time synchronization signal contains the base station direction information and timing information. The terminal detects the main space-time synchronization signal and the auxiliary space-time synchronization signal in the space-time synchronization signal to achieve initial synchronization with the base station and obtain the direction and timing information of the base station, laying the foundation for subsequent communication steps.

[0068] Step S220: Determine the base station direction information and timing time information of the base station based on the space-time synchronization signal.

[0069] The terminal detects the main space-time synchronization signal in the space-time synchronization signal Afterwards, due to The first subcarrier spacing is designed to be , and the system parameters meet , the terminal can successfully capture the PSS using the existing PSS detection algorithm without pre-compensation of frequency offset. , thereby obtaining its timing position, that is, timing time information. After successful capture, the terminal can obtain the timing position of the main space-time synchronization signal, which is the timing time information and is used to complete symbol timing synchronization. Subsequently, the terminal calculates the auxiliary space-time synchronization signal based on the timing position of the main space-time synchronization signal. The terminal uses the existing SSS detection algorithm to process the signal segment and complete the detection of the auxiliary space-time synchronization signal. Since the base station has pre-compensated the auxiliary space-time synchronization signal for frequency offset, and the system design has ensured that the first bandwidth of the space-time synchronization signal meets the following requirements: The terminal can accurately demodulate the auxiliary space-time synchronization signal while maintaining controllable residual frequency offset. Based on the unique index group formed by combining the first index of the primary space-time synchronization signal and the second index of the auxiliary space-time synchronization signal, the terminal uses a table lookup to map it to one of multiple spatial wavebands preconfigured by the system. Each spatial waveband uniquely corresponds to a spatial pointing angle. Through this mapping, the terminal can directly obtain the direction of the satellite base station relative to the terminal, which is used for subsequent receive beam alignment.

[0070] Step S230: After obtaining the base station direction information and timing time information, receive a frequency offset measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency offset measurement signal carries a pilot sequence.

[0071] After successfully obtaining the base station direction information and timing information in step S220, the terminal accurately aligns the receiving beam to the direction of the satellite-borne base station based on the obtained base station direction information (i.e., the azimuth-elevation vector corresponding to the spatial wave position), and based on the timing information (i.e., the main space-time synchronization signal Timing position and auxiliary space-time synchronization signal The terminal then establishes an accurate symbol timing reference based on the start time of the frequency offset measurement signal (the time at which the signal is transmitted). At this point, the terminal has completed initial synchronization and direction alignment, and is capable of stably receiving subsequent signals. Subsequently, the terminal receives the signal in the second bandwidth of the preset beam according to the system pre-configured frequency offset measurement signal period (if the frequency offset measurement signal is transmitted periodically) or the continuous reception mechanism. Internal receiving frequency deviation measurement signal The signal carries a sparse pilot sequence in the frequency domain , the third subcarrier spacing is , and satisfies , ensuring coverage of the maximum Doppler frequency offset range across the entire link. The terminal leverages established timing synchronization to extract the frequency offset measurement signal within the correct time window and estimates the residual Doppler frequency offset through phase or frequency domain processing, providing a basis for frequency offset compensation for subsequent signal demodulation.

[0072] Step S240: performing residual frequency offset compensation on subsequently received downlink signals based on the pilot sequence.

[0073] The terminal extracts the sparse pilot sequence Afterwards, the existing frequency offset estimation algorithm (for example, based on pilot phase rotation or frequency domain correlation) can be used to estimate the residual Doppler frequency offset value. After determining the residual frequency offset estimate, the terminal can use it as the frequency offset compensation amount, and perform residual frequency offset compensation on all subsequently received downlink signals by complex conjugate multiplication or frequency domain rotation. For specific compensation methods, please refer to the relevant technology, which will not be described in detail in the embodiments of this application. After the compensation is completed, the residual frequency offset is eliminated, and the carrier frequency of the downlink signal is aligned with the terminal local oscillator frequency, meeting the frequency offset tolerance requirements required for subsequent demodulation, channel estimation and data detection. The entire compensation process does not require additional signaling from the base station, and is completely completed autonomously by the terminal based on the received pilot sequence.

[0074] Step S250: After detecting the cell access signal, complete terminal access based on the cell access signal.

[0075] After completing residual frequency offset compensation, the terminal continuously aligns its receive beam toward the base station and monitors the cell access signal on a fixed frequency resource pre-set by the system. The cell access signal is transmitted by the base station using an access beam with service-level subcarrier spacing and dynamically scheduled resources. The terminal uses the frequency offset compensation result obtained in step S240 to correct the received signal's frequency offset, ensuring perfect carrier frequency alignment.

[0076] It should be noted that the technology of using existing cell access signals for terminal access is a relatively mature existing technology in this field. For its specific implementation method, please refer to the relevant technology, and the embodiments of this application will not be repeated.

[0077] See Figure 4 Based on the same inventive concept, an embodiment of the present application also provides a terminal access method, which includes: the base station executes the following steps: Step S110: Generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency deviation measurement signal; the time-space synchronization signal carries the base station direction information and timing time information of the base station; the frequency deviation measurement signal carries a pilot sequence; Step S120: Send the cell synchronization auxiliary signal to the terminal, so that the terminal demodulates the cell synchronization auxiliary signal, and performs terminal access based on the demodulated base station direction information, timing time information and pilot sequence. The terminal executes the following steps: Step S210: Receive the space-time synchronization signal in the cell auxiliary synchronization signal sent by the base station; Step S220: Determine the base station direction information and timing time information of the base station based on the space-time synchronization signal; Step S230: After obtaining the base station direction information and timing time information, receive the frequency deviation measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency deviation measurement signal carries a pilot sequence; Step S240: Perform residual frequency deviation compensation on the subsequently received downlink signal based on the pilot sequence; Step S250: After detecting the cell access signal, complete terminal access based on the cell access signal.

[0078] For ease of understanding, the embodiment of the present application provides specific implementation steps of the above-mentioned terminal access method in a certain application scenario by a base station and a terminal, mainly including: Step 1: Configure static parameters of the communication system on the base station side; The static parameters that need to be configured include: (1) Maximum Doppler frequency deviation of the system downlink , calculated using existing methods based on the downlink carrier frequency and the maximum speed of the base station, unit: Hertz; (2) downlink system subcarrier spacing , in Hertz; (3) The maximum difference in Doppler frequency deviation between the center and edge of the downlink beam , calculated using existing methods based on the downlink carrier frequency, the maximum movement speed of the base station, the satellite altitude and the downlink beam coverage, with the unit being Hertz; (4) Performing spatial wave position division: Assuming that the terminal is located at the mean sea level, the entire airspace is divided into no more than 1008 directions from the perspective of the ground terminal, and each direction represents one spatial wave position. Existing technologies can be used for wave position division.

[0079] Step 2: Design cell synchronization auxiliary signal; 1. Space-time synchronization signal: The space-time synchronization signal is used by the terminal to measure the timing of the base station's downlink signal and the direction of the satellite base station relative to the terminal. The design of the space-time synchronization signal includes space-time synchronization sequence Design and transmit subcarrier spacing design, including: time and space synchronization sequence Including master time and space synchronization signal Auxiliary space-time synchronization signal , both use the synchronization sequences PSS and SSS of the existing 5G protocol respectively. and There are 3 and 336 values ​​respectively, and the combination of the two has 1008 combinations. Each combination can represent one spatial wave position. These can be configured before the communication system starts working. The first subcarrier spacing is set to ,in is a positive integer and satisfies , auxiliary space-time synchronization signal The second subcarrier spacing can be directly set to .

[0080] 2. Frequency deviation measurement signal: The frequency deviation measurement signal is used to measure the Doppler frequency deviation of the downlink signal. Its design includes: frequency deviation measurement pilot sequence design and transmit subcarrier spacing design, among which: pilot sequence Any pilot sequence with frequency offset measurement capability in the prior art (e.g., DMRS, SRS, CSIRS) can be used, but the sequence value is pre-configured and known to the terminal. The third transmission subcarrier spacing is ,in is a positive integer and satisfies .

[0081] Step 3: Configure frequency domain resources for cell synchronization auxiliary signals; Assume that the total bandwidth of the access beam is , the bandwidth occupied by the existing signal is , occupied bandwidth refers to the bandwidth resources that may be occupied by existing technologies at any time when the beam is accessed), then the idle bandwidth resources can be expressed as , Idle bandwidth resources refer to bandwidth resources that will not be occupied by existing technologies at all times when the access beam belongs to them. In the idle bandwidth resources, frequency resources for transmitting time-space synchronization signals and frequency offset measurement signals are planned respectively. The frequencies of these two frequency resources are required to be fixed, and the bandwidths are respectively and ,Require: , . Auxiliary space-time synchronization signal sequence The length of the sequence; and Both An integer multiple of .

[0082] Step 4: The base station generates a cell synchronization auxiliary signal; The steps of generating the time-space synchronization signal mainly include: converting the main time-space synchronization signal sequence into the baseband frequency domain Placed in the first bandwidth The center position of the baseband time domain signal is then generated using the method of generating the baseband time domain signal in the existing protocol to generate the main time and space synchronization signal in the baseband time domain. Similarly, in the baseband frequency domain, the auxiliary space-time synchronization signal sequence Placed in the first bandwidth Then, the auxiliary space-time synchronization signal in the baseband time domain is generated using the method of generating the baseband time domain signal in the existing protocol. ; Finally, construct the time-space synchronous baseband time domain signal ,in, and are all one-dimensional row vectors. In addition, it should be noted that due to Subcarrier spacing ratio Small times, so The absolute length of time will be longer than long times.

[0083] The steps for generating the frequency deviation measurement signal mainly include: first, calculating the sequence length Then, the method of generating pilot sequence in the existing protocol is used to generate a length of Pilot measurement pilot sequence , and in Fill after each element 0, get , then Placed in the second bandwidth Finally, the frequency deviation measurement signal in the baseband time domain is generated using the existing protocol to generate the baseband time domain signal. .

[0084] Step 5: The base station transmits a cell synchronization auxiliary signal to the terminal; The base station first transmits The Doppler frequency deviation of the time-space synchronization signal is calculated based on the expected center frequency (the expected center frequency can be calculated by considering the carrier frequency and using the calculation method in the existing protocol), its own position, motion state (including motion direction and motion speed) and downlink beam direction. ; Then use the frequency offset compensation value right Perform frequency offset pre-compensation. After pre-compensation, the transmission , so after frequency offset pre-compensation The transmission frequency will not exceed the first bandwidth In addition, It can be transmitted directly without frequency offset compensation, but The start time needs to be the same as The start time of a certain cycle is aligned. In addition, it should be noted that as long as the access beam is in operation, it will continue to transmit the cell synchronization auxiliary signal. The time and space synchronization signal is transmitted in a continuous cycle (with no time interval between different cycles). The frequency offset measurement signal can be transmitted continuously or periodically. If it is transmitted periodically, the transmission period information is also preset by the communication system and known to the terminal.

[0085] Step 6: The terminal detects the time and space synchronization signal; The terminal uses existing technology (such as random beam scanning or fixed order beam scanning) to continuously receive downlink signals; then, the PSS signal detection method of the existing technology is used to detect After successful detection, you can get The timing position of Timing position ( The start time is End time); secondly, intercept Receive the signal and use the existing SSS signal detection method to complete detection; finally, the direction information of the satellite base station is obtained based on the detection results of the two.

[0086] In the above-mentioned terminal detection process, since the base station has pre-compensated the Doppler frequency offset of the time-space synchronization signal, although the pre-compensation is completed based on the downlink beam center position (that is, the downlink beam direction), this may cause the terminal to still have residual frequency offset after receiving the time-space synchronization signal (the terminal may be located at a random position within the beam coverage range). However, since the system parameters are designed to ensure that , that is, the residual frequency deviation is generally not greater than Subcarrier spacing, and the existing technology of PSS sequence detection can correct the maximum half subcarrier frequency deviation, so the terminal can use the existing technology to complete Demodulation.

[0087] Step 7: Terminal frequency offset measurement; After the terminal completes the detection of the time-space synchronization signal, it obtains the direction and timing information of the satellite base station. Next, the terminal can align the receiving beam with the direction of the satellite base station and then configure the receiving frequency deviation measurement signal based on the timing time and the period of the frequency deviation measurement signal. After receiving the frequency deviation measurement signal, the terminal can use existing technology to complete the Doppler frequency deviation measurement. The third transmission subcarrier spacing satisfies , that is, the maximum Doppler frequency offset will not be greater than half of the frequency offset measurement pilot subcarrier interval, and the existing frequency offset measurement technology can estimate the frequency offset of the maximum half subcarrier, so the terminal can use the existing frequency offset measurement technology to complete the Doppler frequency offset compensation.

[0088] Step 8: The terminal completes access; The terminal aligns the receiving beam direction with the satellite base station to continuously receive signals and uses the frequency offset measurement results to pre-compensate the received signal for frequency offset. It then uses existing technology to detect the cell access signal broadcast by the satellite base station and complete the subsequent access process.

[0089] See Figure 5Based on the same inventive concept, an embodiment of the present application also provides a base station 300, including: a cell synchronization auxiliary signal generation module 310, used to generate a cell synchronization auxiliary signal; wherein, the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency deviation measurement signal; the time-space synchronization signal carries the base station direction information and timing time information of the base station; the frequency deviation measurement signal carries a pilot sequence; a cell synchronization auxiliary signal sending module 320, used to send a cell synchronization auxiliary signal to a terminal, so that the terminal demodulates the cell synchronization auxiliary signal, and performs terminal access based on the demodulated base station direction information, the timing time information and the pilot sequence.

[0090] Optionally, the space-time synchronization signal includes a main space-time synchronization signal and an auxiliary space-time synchronization signal; the above-mentioned cell synchronization auxiliary signal generation module 310 is specifically used to: obtain a main space-time synchronization signal sequence and an auxiliary space-time synchronization signal sequence; in the baseband frequency domain, map the main space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and perform modulation processing to obtain the main space-time synchronization signal; in the baseband frequency domain, map the auxiliary space-time synchronization signal sequence to the center subcarrier position of the first bandwidth of the preset beam, and perform modulation processing to obtain the auxiliary space-time synchronization signal.

[0091] Optionally, the base station direction information of the base station includes spatial wave positions; the above-mentioned cell synchronization auxiliary signal generation module 310 is specifically used to: after obtaining the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence, obtain the first index of the main space-time synchronization signal sequence and the second index of the auxiliary space-time synchronization signal sequence; based on the first index and the second index, obtain the index group of the synchronization signal sequence group composed of the main space-time synchronization signal sequence and the auxiliary space-time synchronization signal sequence; assign a spatial wave position uniquely corresponding to each index group; wherein the spatial wave position is used to indicate the spatial pointing of the base station relative to the terminal.

[0092] Optionally, the above-mentioned base station 300 also includes: a first subcarrier spacing determination module, used to determine the first subcarrier spacing of the main space-time synchronization signal based on the system downlink subcarrier spacing; wherein the system downlink subcarrier spacing is determined by the system frame structure; the first subcarrier spacing is smaller than the system downlink subcarrier spacing, and the first subcarrier spacing is larger than the intra-beam frequency offset protection interval; the intra-beam frequency offset protection interval is used to characterize the minimum frequency domain protection interval required by the terminal within the coverage range of the same beam, and the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency offset between the downlink beam center and the downlink beam edge position.

[0093] Optionally, the above-mentioned base station 300 also includes: a second subcarrier spacing determination module, used to determine the second subcarrier spacing of the auxiliary space-time synchronization signal based on the system downlink subcarrier spacing; wherein, the system downlink subcarrier spacing is determined by the system frame structure; the second subcarrier spacing is equal to the system downlink subcarrier spacing.

[0094] Optionally, the above-mentioned base station 300 also includes: a first bandwidth determination module, used to determine the first bandwidth of the space-time synchronization signal; wherein, the first bandwidth is not less than the minimum frequency domain protection bandwidth; the minimum frequency domain protection bandwidth is determined based on the occupied bandwidth of the space-time synchronization signal and the full-link frequency offset protection bandwidth; the full-link frequency offset protection bandwidth is determined based on the system downlink maximum Doppler frequency offset.

[0095] Optionally, the above-mentioned base station 300 also includes: a frequency deviation pre-compensation module, which is used to determine the Doppler frequency deviation of the space-time synchronization signal based on the expected center frequency, base station position, base station motion status and downlink beam direction of the space-time synchronization signal; and perform frequency deviation pre-compensation on the auxiliary space-time synchronization signal based on the Doppler frequency deviation.

[0096] Optionally, the above-mentioned cell synchronization auxiliary signal generation module 310 is specifically used to: determine the sequence length of the pilot sequence based on the third subcarrier spacing of the frequency deviation measurement signal and the second bandwidth of the frequency deviation measurement signal; generate the pilot sequence based on the sequence length; sparsely sample the pilot sequence to obtain the pilot sequence that is sparse in the frequency domain; in the baseband frequency domain, map the pilot sequence to the central subcarrier position of the second bandwidth of the preset beam, and perform modulation processing to obtain the frequency deviation measurement signal.

[0097] Optionally, the above-mentioned base station 300 also includes: a third subcarrier spacing determination module, used to determine the third subcarrier spacing of the frequency domain measurement signal; wherein, the third subcarrier spacing is greater than the full-link frequency offset protection bandwidth; wherein, the full-link frequency offset protection bandwidth is determined based on the system downlink maximum Doppler frequency offset.

[0098] Optionally, the preset beam is an access beam; wherein, the access beam is a downlink beam used for initial access in the base station; the above-mentioned cell synchronization auxiliary signal sending module 320 is specifically used to: utilize the idle bandwidth resources in the access beam to send a cell synchronization auxiliary signal to the terminal; wherein, the sum of the first bandwidth of the space-time synchronization signal and the second bandwidth of the frequency deviation measurement signal is not greater than the idle bandwidth resources.

[0099] Optionally, the cell synchronization auxiliary signal sending module 320 is specifically configured to: continuously send a time and space synchronization signal to the terminal; and continuously or periodically send a frequency offset measurement signal to the terminal.

[0100] See Figure 6 Based on the same inventive concept, an embodiment of the present application also provides a terminal 400, including: a space-time synchronization signal receiving module 410, used to receive the space-time synchronization signal in the cell auxiliary synchronization signal sent by the base station; a space-time synchronization signal demodulation module 420, used to determine the base station direction information and timing time information of the base station based on the space-time synchronization signal; a frequency deviation measurement signal receiving module 430, used to receive the frequency deviation measurement signal in the cell auxiliary synchronization signal sent by the base station after obtaining the base station direction information and the timing time information; wherein, the frequency deviation measurement signal carries a pilot sequence; a residual frequency deviation compensation module 440, used to perform residual frequency deviation compensation on the subsequently received downlink signal based on the pilot sequence; a terminal access module 450, used to complete terminal access based on the cell access signal after detecting the cell access signal.

[0101] Based on the same inventive concept, an embodiment of the present application also provides a non-terrestrial communication system, including a base station 300 provided in an embodiment of the present application and a terminal 400 provided in an embodiment of the present application, wherein the base station 300 is communicatively connected to the terminal 400.

[0102] Please refer to Figure 7 , Figure 7 This is a structural block diagram of an electronic device provided in an embodiment of the present application. The electronic device 500 includes: at least one processor 510, at least one memory 520, at least one communication interface 530, and at least one communication bus 540. Among them, the communication bus 540 is used to realize direct connection and communication between these components, the communication interface 530 is used to communicate signaling or data with other node devices, and the memory 520 stores machine-readable instructions executable by the processor 510. When the electronic device 500 is running, the processor 510 communicates with the memory 520 through the communication bus 540, and when the machine-readable instructions are called by the processor 510, the terminal access method applied to the base station or the terminal access method applied to the terminal is executed.

[0103] As an implementation example, when the machine-readable instructions in the electronic device 500 are invoked by the processor 510 to execute the aforementioned terminal access method applied to a base station, the electronic device 500 may be a base station, and the terminal may be wirelessly connected to the base station. The base station may also connect to or transmit and receive information with the Evolved Universal Terrestrial Radio Access (E-UTRA) system, the New Radio (NR) system, future wireless access systems, or a WiFi system defined in the 3rd Generation Partnership Project (3GPP). The base station may also connect to devices in two or more of the aforementioned different wireless access systems. The base station may also connect to an Open Radio Access Network (O-RAN). The base station may be configured with a module for implementing base station functions. The module for implementing base station functions can implement the functions of the following devices: a base station, an evolved NodeB (eNodeB or eNB), a transmission reception point (TRP), a next-generation NodeB (gNB) in a fifth-generation (5G) mobile communication system, a next-generation base station in a sixth-generation (6G) mobile communication system, a base station in a future mobile communication system, or an access node in a WiFi system. The aforementioned base station may also include an antenna and a transceiver. In the uplink, uplink signals from terminals are received via the antenna, modulated by the transceiver, and further processed by the processor 510 to recover the signaling information sent by the terminal. In the downlink, signaling messages are processed by the processor 510 and modulated by the transceiver to generate downlink signals, which are then transmitted to the terminal via the antenna. The processor 510 is also configured to execute the terminal access method applied to a base station as described in the above embodiments. The base station may include a macro base station, a micro base station, an indoor base station, a relay node, or a donor node. It can be understood that the above only introduces a simplified design of the base station. In actual applications, the base station may include any number of transmitters, receivers, processors, controllers, memories, communication units, etc., and all base stations that can implement this application are within the scope of protection of this application.

[0104] As an embodiment, when the machine-readable instructions in the electronic device 500 are called by the processor 510 to execute the terminal access method applied to the terminal, the electronic device 500 may be a terminal, and different terminals may be connected to each other via wired or wireless means. The terminal can be widely used in various scenarios, such as near field communications (NFC), device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart office, smart wearables, smart transportation, smart city, etc. The terminal may also be referred to as a mobile station (MS), terminal, or terminal equipment, and may also include a subscriber unit (SU), a cellular phone, a smart phone, a wireless data card, a personal digital assistant (PDA), a tablet computer, a wireless modem, a handheld device, a laptop computer, a cordless phone, or a wireless local loop (WLL) station, a machine type communication (MTC) terminal, etc. For ease of description, in all embodiments of the present application, the device terminal mentioned above may also include an antenna and a transceiver. The transceiver conditions (e.g., performs analog-to-analog conversion, filtering, amplification, and upconversion) the output samples and generates an uplink signal, which is transmitted via an antenna to the network device. On the downlink, the antenna receives the downlink signal transmitted by the network device, and the transceiver conditions (e.g., performs filtering, amplification, downconversion, and digitization) the signal received from the antenna and provides input samples. The processor 510 is configured to execute the terminal access method described in the above embodiments for a terminal. The embodiments of this application do not limit the specific technology or device form factor employed by the terminal.

[0105] The processor 510 includes one or more processors, which may be an integrated circuit chip with signal processing capabilities. The processor 510 may be a general-purpose processor, including a central processing unit (CPU), a microcontroller unit (MCU), a network processor (NP), or other conventional processors; or a dedicated processor, including a neural network processing unit (NPU), a graphics processing unit (GPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. Furthermore, when there are multiple processors 510, some may be general-purpose processors, while others may be dedicated processors. The memory 520 includes one or more, which may be, but is not limited to, random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.

[0106] An embodiment of the present application further provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer program instructions. When the computer program instructions are executed by a computer, the computer is caused to perform various functions or steps in the above-mentioned terminal access method embodiment.

[0107] The embodiment of the present application further provides a computer program product, which, when executed on a computer, enables the computer to execute the various functions or steps in the above-mentioned terminal access method embodiment.

[0108] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A terminal access method, characterized in that: Applied to a base station, the method includes: Generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency offset measurement signal; the time-space synchronization signal carries base station direction information and timing information of the base station; the frequency offset measurement signal carries a pilot sequence; A cell synchronization auxiliary signal is sent to the terminal, so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, the timing time information, and the pilot sequence.

2. The terminal access method according to claim 1, wherein: The space-time synchronization signal includes a primary space-time synchronization signal and a secondary space-time synchronization signal; The method for determining the space-time synchronization signal includes: Acquire a primary space-time synchronization signal sequence and a secondary space-time synchronization signal sequence; In the baseband frequency domain, mapping the primary space-time synchronization signal sequence to the central subcarrier position of the first bandwidth of the preset beam, and performing modulation processing to obtain the primary space-time synchronization signal; In the baseband frequency domain, the secondary space-time synchronization signal sequence is mapped to the central subcarrier position of the first bandwidth of the preset beam, and modulation processing is performed to obtain the secondary space-time synchronization signal.

3. The terminal access method according to claim 2, wherein: The base station direction information of the base station includes spatial wave position; After acquiring the primary space-time synchronization signal sequence and the secondary space-time synchronization signal sequence, the method further includes: Acquire a first index of the primary space-time synchronization signal sequence and a second index of the secondary space-time synchronization signal sequence; Based on the first index and the second index, obtaining an index group of a synchronization signal sequence group consisting of the primary space-time synchronization signal sequence and the secondary space-time synchronization signal sequence; A uniquely corresponding spatial wave position is allocated to each index group; wherein the spatial wave position is used to indicate the spatial orientation of the base station relative to the terminal.

4. The terminal access method according to claim 2, wherein: The method further comprises: Based on the system downlink subcarrier spacing, the first subcarrier spacing of the main space-time synchronization signal is determined; wherein, the system downlink subcarrier spacing is determined by the system frame structure; the first subcarrier spacing is smaller than the system downlink subcarrier spacing, and the first subcarrier spacing is larger than the intra-beam frequency offset protection interval; the intra-beam frequency offset protection interval is used to characterize the minimum frequency domain protection interval required by the terminal within the coverage range of the same beam, and the intra-beam frequency offset protection interval is determined based on the maximum difference in Doppler frequency offset between the downlink beam center and the downlink beam edge.

5. The terminal access method according to claim 2, wherein: The method further comprises: Based on the system downlink subcarrier spacing, a second subcarrier spacing of the secondary space-time synchronization signal is determined; wherein the system downlink subcarrier spacing is determined by the system frame structure; and the second subcarrier spacing is equal to the system downlink subcarrier spacing.

6. The terminal access method according to claim 2, wherein: The method further comprises: Determine the first bandwidth of the space-time synchronization signal; wherein, the first bandwidth is not less than the minimum frequency domain protection bandwidth; the minimum frequency domain protection bandwidth is determined based on the occupied bandwidth of the space-time synchronization signal and the full-link frequency offset protection bandwidth; the full-link frequency offset protection bandwidth is determined based on the system downlink maximum Doppler frequency offset.

7. The terminal access method according to claim 2, wherein: Before sending the cell synchronization auxiliary signal to the terminal, the method further includes: Determining a Doppler frequency offset of the space-time synchronization signal based on an expected center frequency of the space-time synchronization signal, a base station position, a base station motion state, and a downlink beam direction; Based on the Doppler frequency offset, frequency offset pre-compensation is performed on the auxiliary space-time synchronization signal.

8. The terminal access method according to claim 1, wherein: The method for determining the frequency deviation measurement signal includes: determining a sequence length of a pilot sequence based on a third subcarrier spacing of the frequency offset measurement signal and a second bandwidth of the frequency offset measurement signal; generating the pilot sequence based on the sequence length; Performing sparse sampling on the pilot sequence to obtain a frequency-domain sparse pilot sequence; In the baseband frequency domain, the pilot sequence is mapped to a central subcarrier position of a second bandwidth of a preset beam, and modulation processing is performed to obtain the frequency offset measurement signal.

9. The terminal access method according to claim 8, characterized in that: The method further comprises: Determine the third subcarrier spacing of the frequency domain measurement signal; wherein, the third subcarrier spacing is greater than the full-link frequency offset protection bandwidth; wherein, the full-link frequency offset protection bandwidth is determined based on the system downlink maximum Doppler frequency offset.

10. The terminal access method according to any one of claims 2 to 9, characterized in that: The preset beam is an access beam; wherein the access beam is a downlink beam used for initial access in the base station; The sending of the cell synchronization auxiliary signal to the terminal includes: A cell synchronization auxiliary signal is sent to the terminal using idle bandwidth resources in the access beam; wherein the sum of the first bandwidth of the space-time synchronization signal and the second bandwidth of the frequency offset measurement signal is not greater than the idle bandwidth resources.

11. The terminal access method according to any one of claims 1 to 9, characterized in that: The sending of the cell synchronization auxiliary signal to the terminal includes: Continuously send time and space synchronization signals to the terminal; A frequency deviation measurement signal is continuously or periodically sent to the terminal.

12. A terminal access method, characterized in that: Applied to a terminal, the method includes: Receiving a time and space synchronization signal in a cell auxiliary synchronization signal sent by a base station; Determining base station direction information and timing time information of the base station based on the space-time synchronization signal; After obtaining the base station direction information and the timing time information, receiving a frequency offset measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency offset measurement signal carries a pilot sequence; performing residual frequency offset compensation on a subsequently received downlink signal based on the pilot sequence; After detecting the cell access signal, terminal access is completed based on the cell access signal.

13. A terminal access method, characterized in that: The method comprises: The base station performs the following steps: Generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency offset measurement signal; the time-space synchronization signal carries base station direction information and timing information of the base station; the frequency offset measurement signal carries a pilot sequence; Sending a cell synchronization auxiliary signal to a terminal, so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, the timing time information, and the pilot sequence; The terminal performs the following steps: receiving the space-time synchronization signal in the cell auxiliary synchronization signal sent by the base station; Determining the base station direction information and the timing time information of the base station based on the space-time synchronization signal; After obtaining the base station direction information and the timing time information, receiving the frequency offset measurement signal in the cell auxiliary synchronization signal sent by the base station; wherein the frequency offset measurement signal carries the pilot sequence; performing residual frequency offset compensation on a subsequently received downlink signal based on the pilot sequence; After detecting the cell access signal, terminal access is completed based on the cell access signal.

14. A base station, characterized in that: include: A cell synchronization auxiliary signal generation module, configured to generate a cell synchronization auxiliary signal; wherein the cell synchronization auxiliary signal includes a time-space synchronization signal and a frequency offset measurement signal; the time-space synchronization signal carries base station direction information and timing information of the base station; and the frequency offset measurement signal carries a pilot sequence; The cell synchronization auxiliary signal sending module is used to send a cell synchronization auxiliary signal to the terminal, so that the terminal demodulates the cell synchronization auxiliary signal and performs terminal access based on the demodulated base station direction information, the timing time information and the pilot sequence.

15. A terminal, characterized in that: include: A time-space synchronization signal receiving module, configured to receive a time-space synchronization signal in a cell auxiliary synchronization signal sent by a base station; a space-time synchronization signal demodulation module, configured to determine base station direction information and timing time information of the base station based on the space-time synchronization signal; A frequency offset measurement signal receiving module, configured to receive a frequency offset measurement signal in the cell auxiliary synchronization signal sent by the base station after obtaining the base station direction information and the timing time information; wherein the frequency offset measurement signal carries a pilot sequence; a residual frequency offset compensation module, configured to perform residual frequency offset compensation on subsequently received downlink signals based on the pilot sequence; The terminal access module is used to complete terminal access based on the cell access signal after detecting the cell access signal.

16. A non-terrestrial communication system, characterized in that: include: The base station according to claim 14 and the terminal according to claim 15, wherein the terminal is communicatively connected to the base station.

17. An electronic device, characterized in that: include: A processor, a memory and a communication bus, wherein the processor and the memory communicate with each other via the communication bus; The memory stores program instructions that can be executed by the processor, and the processor can execute the method according to any one of claims 1 to 13 by calling the program instructions.

18. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, which, when executed by a computer, enable the computer to perform the method according to any one of claims 1 to 13.

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